adjusting your TPS AND IAC

Discussion in 'Engine: Repairs and Modifications & generally corv' started by grumpyvette, Sep 19, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    yes IM well aware theres a great deal of links with info you need to read that you'll most likely skip over,.....
    theres a great deal of additional info in the links and sub-links posted in the thread below.when you find you've got questions or just want to fully understand the process reading the links provides you with the required info, so ID strongly suggest taking the time to read thru them, as you'll be amazed at what they contain.
    the prime symptoms of a defective IAC is an engine that either won,t idle at a consistent RPM,or it won,t keep running, or it just changes speeds and won,t settle down almost like a vacume leak, a defective or badly adjusted or defective TPS tends to result in a loss of engine response and either fouled plugs or plugs showing excessively lean combustion.
    the TPS is easily checked with a multi meter, the IAC can be removed and cleaned, as will the throttle body its installed in, but these do go bad and need replacing

    SKIPPING OR NOT READING LINKED INFO ON THIS WEB SITE IS ALWAYS A BAD IDEA

    http://repairs.willcoxcorvette.com/1985-1989-corvette-idle-to-air-mixture-adjustment-procedure/


    http://garage.grumpysperformance.co...-cranks-but-won-t-start-intermittently.14212/



    Start and run engine until it reaches operating temperature (closed loop)
    Check and set ignition timing to 6 degrees before dead center (BDC) with tan EST wire disconnected
    Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
    Jumper terminals "A" and "B" on the ALDL
    Turn ignition key on and do not start engine
    Wait 60 seconds so that the idle air control (IAC) motor fully extends
    Without turning ignition key off, remove connector from IAC motor
    Turn ignition key off and disconnect ALDL jumper
    Attach external RPM meter using Tach port or scanner using ALDL port
    Start and run engine until it reaches operating temperature (closed loop)
    Remove minimum idle air cap using awl if required
    Adjust idle speed to 425 (+/- 25) rpm in either in park or neutral
    Turn ignition key off and reconnect EST wire and IAC motor
    Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
    Reset ECM by disconnecting and reconnecting power at battery terminal
    Depress accelerator pedal slightly
    Start and run engine for 5 seconds
    Turn ignition key off for 10 seconds
    Drive vehicle to assist in ECM reprogramming
    If you used a scanner, you should see around 20 IAC steps


    http://www.ecklerscorvette.com/corvette-idle-air-control-tool-sensor-test-1985-1993.html
    [​IMG]


    I found these bits of linked info that may be useful.
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]
    YES THERE'S SEVERAL SUB LINKS
    (IN MOST OF THE THREADS)
    THEY ALL CONTAIN A BIT DIFFERENT RELATED INFO YOU'LL NEED

    ANYTIME YOUR DEALING WITH THE ENGINE AND HOW IT RUNS ,
    YOULL BE DEALING WITH DIFFERENT ISSUES,
    COOLANT AND OIL TEMPS,& PRESSURE
    FUEL PRESSURE , INJECTOR FUNCTION
    FUEL DELIVERY, PRESSURE & VOLUME
    RELATED FUEL / AIR RATIO
    EFFECTIVE COMPRESSION & RING SEAL
    VALVE TIMING & LIFT & DURATION & VALVE SEAL
    IGNITION SPARK TIMING & STRENGTH, & IGNITION ADVANCE CURVE
    EXHAUST BACK PRESSURE
    SENSOR OUTPUT TO THE CPU
    VOLTAGE & GROUNDS
    http://www.thirdgen.org/tpimod2

    http://www.batee.com/corvette/dcrg/read ... s_sim5.htm

    viewtopic.php?f=80&t=728&p=1243&hilit=electrical+connectors#p1243



    viewtopic.php?f=32&t=6550&p=20807#p20807

    http://www.mamotorworks.com/corvette-c4 ... 6-903.html

    http://www.docstoc.com/docs/25331704/Co ... u-1992-Not

    viewtopic.php?f=55&t=5307&p=15751&hilit=runners+gaskets+leak#p15751

    http://www.iroczone.com/techarttpsadj.html

    http://www.haltech.com/product/platinum ... /sport-gm/

    http://temp.corvetteforum.net/c4/vader86/tpsiac.html

    http://www.golenengineservice.com/html/tps.html

    http://www.s-series.org/htm/how2/tpsadjust.htm

    viewtopic.php?f=3&t=330&p=5167&hilit=start+sequence#p5167

    http://www.jcwhitney.com/autoparts/Sear ... p=ZX503796

    http://www.summitracing.com/parts/SUN-CP9001

    viewtopic.php?f=44&t=366&p=448#p448

    http://www.etoolcart.com/autoxray-scann ... x6000.aspx

    viewtopic.php?f=55&t=1475&p=3325#p3325

    http://www.corvetteactioncenter.com/kb/ ... Idle+Speed

    http://www.thirdgen.org/tpimod1
    http://www.ecklerscorvette.com/corvette ... 1991.html#

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]



    http://corvette.stealing-fire.com/tps_diagnostics.htm

    The TPS (Throttle Position Sensor) on my 1985 Corvette bit the dust after 18 years. I purchased a new one from a local dealership and installed it. In the two years following its replacement, I noticed an erratic idle that got progressively worse. Like most people would do, I refused to believe the TPS was bad because it was "new" even though the cars computer was throwing Code 21's (TPS Signal Voltage High.)

    However, when I checked the TPS voltage at idle it was not the .54 volts I expected and nowhere near the .54 volts that I had originally set it to about two years prior, but 2.5 volts.

    I searched my GM Corvette service manual and discovered that they only specify an "on-car" diagnostic for the TPS. Needless to say their diagnostic showed the TPS to be bad.

    After looking at the schematic for the TPS (below) I could see that it was just a variable potentiometer. GM did not include any specifications for the resistance values if you simply wanted to "ohm it out." Out of curiosity I measured the resistance between pins A & C and discovered that the circuit was completely open unless I placed some sideward pressure on the pins, then I would get a reading. Clearly I had an intermittent connection inside the TPS.

    [​IMG]

    I then measured the resistance between pins B & C and saw that there was a measurable resistance that changed as the TPS actuator arm was moved. This was to be expected.

    Without a good path to ground on pin A, the 5 volt reference could not be pulled to ground and so the TPS potentiometer could not return a variable voltage on the wiper contact B.

    So, here's the pertinent info:

    With a new TPS in hand (Part # 1711-1606) I've documented the values that you should see if you want to do a quick TPS check with an ohm meter:

    TPS Actuator Arm at rest: Pins Values (ohms)
    A to C = 5.88k
    A to B = 2.44k
    C to B = 8.32k

    Rotating the TPS Actuator Arm: At Rest [​IMG] Rotated
    A to B = 2.44k 8.26k
    C to B = 8.32k 2.39k
    [​IMG]

    Final Notes:

    An observant reader might wonder how the ohm value across pins A & B or pins C & B can be greater than the ohm value across pins A & C? Well after opening up my old TPS I've discovered that it isn't quite as simple internally as the schematic diagram would lead you to believe. There's actually two wiper elements inside the TPS and two resistive elements. I'm not going to draw a diagram as it is beyond the scope of this article. Suffice it to say that the TPS works as shown in the schematic but is not constructed as shown in the schematic.

    After installing the new TPS, several anomalies disappeared:

    1) Random high 1,400 RPM idle
    2) Random ECM Code 21's
    3) Random loss of 4+3 overdrive

    The random loss of the overdrive is a curiosity to me. I can only guess that the bad TPS was making the ECM think I was flooring the accelerator and causing the 4+3 overdrive to kick-out.

    Because so much of what the ECM (Electronic Control Module) (computer) does is dependent upon a working Throttle Position Sensor I thought it would be good to provide a little more info to the Corvette hobbyist than what is found in the GM service manuals.

    Also, this info applies only to 1985 models, in particular, mine. It may be applicable to later years, but I have no way of determining this.

    [​IMG]

    http://www.chevythunder.com/fuel injection elect. pg B.htm

    [​IMG]
    [​IMG]
    [​IMG]

    [​IMG]
    http://www.chevythunder.com/fuel injection elect. pg B.htm

    [​IMG]
    [​IMG]
    1st, the IAC motor is not a sensor, it's an actuator.
    2nd, yes, engine can run without it if waiting for a new one.
    3rd, ensure the idle speed screw is set to achieve an IAC position of around 5-10 counts at hot idle.
    4th, ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring.
    5th, IAC TEST: When turning off the engine, watch the IAC pintle; it should fully close, then open halfway.



    [​IMG]

    ONE WAY
    IAC and TPS Adjustment
    Tom Keliher
    Idle Air Control
    Tools needed:

    Torx bit # T-20
    Paper Clip
    Small Punch

    Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.

    Turn on the ignition, but don't start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.

    Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450-500 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

    Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).

    If you set an SES light by having the IAC disconnected, then after shutting down the engine disconnect the negative battery terminal. Wait 5 minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.

    Throttle Position Switch (TPS)
    Tools needed:

    Digital Volt-Ohm-Meter (VOM)
    Jumper Wires (make your own)
    Auto Xray Scanner (if available) will eliminate the need for VOM and jumper wires.

    Turn on ignition, but don't start the engine.

    With a scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.075Volts

    With VOM and jumper wires: disconnect the connector from the TPS. Using your jumper wires, make a connection allowing some room for the VOM terminals to contact the jumper leads and read the TPS voltage.

    If out of spec, loosen the two screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, that could mean a bad TPS switch and could be a cause of stumbling and drive ability problems.

    After setting the correct voltage, turn off ignition switch. Remove jumpers/scanner and reconnect the TPS connector as required.

    be sure you've checked the ignition timing with a decent timing light


    SECOND EXPLANATION


    Tools needed:

    Torx bits or drivers (T-10, T-15, maybe more depending on the application)
    Voltmeter (digital is best, but a really accurate analog will work)
    Tachometer (the one in the vehicle will work fine if equipped)
    Wrenches and an awl (various sizes, only if the idle speed hasn’t ever been set)

    Theory of Operation – (lengthy)

    A common myth about fuel injected vehicles is that the idle speed is fixed and cannot be adjusted. This isnt quite true; there is a setting. It's called minimum air, which is adjustable on TBI and MPFI vehicles. This setting sets the lowest-possible idle speed for the vehicle. The ECM uses the IAC (idle air controller) to raise the idle speed from this adjustment. So, while the exact idle speed isn’t really adjustable, the minimum idle speed is.

    Why adjust the idle speed? Isnt the ECM supposed to do that? Yes it does and it does do a good job, but has to have a starting point. That starting point is called minimum air, or the smallest amount of air allowed to enter the engine with the throttle closed. The ECM can only add air to that minimum setting. If that setting is too high, the ECM cant slow the engine down to an acceptable idle. If the setting is too low, the ECM may not be able to keep the engine running under certain conditions.

    Another reason to adjust minimum air is if there has been some repairs to the fuel system. If the throttle body has been removed (i.e. rebuilt or cleaned) or the TPS (throttle position sensor) has been replaced or otherwise disturbed (i.e. loosened the mounting screws unintentionally -- it happens) then minimum air should be adjusted. Any changes that could affect idle speed or idle quality, like performance upgrades or replacing leaking vacuum lines, should be followed by setting minimum air. If youve got an early year TPI , thats designed to use a 9th cold start injector,check the cold start injector as its a potential problem source if its not working correctly.

    This adjustment, once learned, only takes a few minutes. It rarely has to be adjusted, but it takes so little time to check (and adjust, if needed) that there’s no reason not to do so.



    Checking & Adjustment Instructions

    To establish minimum air, the idle speed must be set first. The idle speed screw is sealed with a cap from the factory. This should be removed by removing the throttle body and using an awl to pry the plug off. If this seems scary, have it done. It’s not difficult but it’s not worth risking damage to the throttle body or human flesh to remove the plug. Once the plug has been removed, reinstall the throttle body.

    Assuming the idle speed screw is accessible and the throttle body is installed, jumper pins A&B on the ALDL (Assembly Line Data Link) connector under the dash. Pins A&B are on the upper-right-hand side. These are the same two pins to jumper to read codes from the ECM. Now turn the key on (the Check Engine light should be lit) and leave the key on for at least 30 seconds. The computer will extend the IAC plunger all the way out to allow adjustment of the idle speed.

    After the 30 second wait, unplug the IAC (square 4-pin connector on the throttle body) WHILE THE KEY IS STILL ON. This prevents the ECM from adjusting the idle speed while you make your adjustments.

    Block the drive wheels, set the emergency brake, and start the engine. Set the idle speed by adjusting the idle speed screw. The engine should be at operating temperature for this. The exact setting is on the emissions label on the radiator shroud, but in general, the idle speed should be about 500 RPM in Drive, 700 in Park / Neutral, or if you have a manual transmission, somewhere between 600-800 RPM. Remember that the truck is running during this adjustment, so stay clear of the fan, and make sure it can’t roll or otherwise be put into gear while this is done.

    Once the minimum idle speed is set, turn the engine off, reconnect the IAC, and remove the jumper from the ALDL connector. The TPS minimum voltage must now be set. Turning the idle-speed screw may have moved the TPS idle voltage away from the specification, so it should be adjusted next.

    Connect a voltmeter between pins A (usually dark blue) and B (usually black, or black/pink) of the TPS, and turn the key on. Dont start the engine. Loosen the two torx screws holding the TPS in place, but don’t remove them. Rotate the TPS until the voltmeter reads between 0.45 and 0.55 volts, with 0.50 being ideal. Tighten the mounting screws (carefully, they thread into soft aluminum) and re-check the voltage to make sure it’s still within range.

    Thats it. After the procedure is done once, its easy to remember and do. I hope this helps.

    take it a step at a time,set the fuel pressure at 40psi, check for vacuum leaks, and adjust the IAC and TPS and set the timing at 8 degrees per the manual,then drive it for 30 minutes to let the computer learn the conditions it operates in

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=875

    http://forum.grumpysperformance.com/viewtopic.php?f=50&t=821&p=1212&hilit=propane+leaks#p1212

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401

    http://forum.grumpysperformance.com/viewtopic.php?f=70&t=1809
    WATCH THE VIDEO, READ THE LINKS
    http://www.youtube.com/watch?v=9CPqbaSg ... re=related

    a propane torch is both safer and easier to use as a method to locate vacuum leaks, and most surging IS related to defective injectors or vacuum leaks
    [​IMG]
    (DONT LIGHT IT) just SLIGHTLY open the valve so its allowing gas to flow at a low volume,start the engine and let it idle at the lowest speed you can then place the tip of the UNLIT torch at any suspected vacuum leak and listen for the rpms to increase and watch the tachometer, gas flowing into a vacuum leak will increase engine speed.
    look for loose or missing vacuum hoses, cracked or broken power brake connections, emissions system hoses that are loose, vacuum connections to the trans or ignition, loose connectors missing or loose bolts cracked hoses missing assessory connections etc.
    naturally this only locates leaks to the outside, and its possible for the intake to suck air from the lifter gallery, so that also needs to be checked if everything else seems to be ok.

    read this
    viewtopic.php?f=44&t=464

    http://www.centuryperformance.com/tunin ... g-148.html
     
    Last edited by a moderator: Oct 9, 2018
  2. grumpyvette

    grumpyvette Administrator Staff Member

    the picture link

    http://shbox.com/1/iac2.jpg

    http://www.thirdgen.org/tpimod2

    yeah thats the problem with EFI, your taught the CPU and codes will locate the problems and point to the source, but its not always the case and theres a zillion things that cause problems that the trouble codes and sensors won,t point too!, in fact theres things that the trouble codes indicate as deffective that may not be!

    these LINKS POSTED HERE, are your friends
    http://garage.grumpysperformance.co...questions-can-be-found-here.12892/#post-66934

    http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-900010&N=700+115&autoview=sku

    http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-800299&N=700+115&autoview=sku

    http://www.rbracing-rsr.com/rsrgauge.htm

    http://garage.grumpysperformance.co...lay-switch-locations-and-info.728/#post-54562

    http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM-G1059&N=700+-114183+115&autoview=sku

    http://www.raytek-northamerica.com/...9b6820919c/1017348120/80_Bro_1-1501_Rev_H.pdf

    http://www.centuryperformance.com/vacuum.asp

    http://www.amazon.com/Corvette-Inje...918205?ie=UTF8&s=books&qid=1181824450&sr=8-15


    KNOWING WHAT YOUR DOING IS IMPORTANT, TO GETTING GOOD RESULTS!
    no one knows everything about all models and years so it helps to have the correct procedures and info in a handy referace source,now you can get by with a HAYNES or CHILTONS manual, or something similar, but for detailed info, OWNING the CHEVY SHOP MANUAL FOR YOUR SPECIFIC CAR IS ALMOST MANDATORY!
    I get asked frequently, "how did you know how to do that?"
    well, EXPERIANCE plays a big roll, working on similar cars and engines helps, and the INTERNET is a good resource... but theres ALWAYS a big need for DETAILED REFERANCE MATERIAL, SPECIFICALLY MATCHING YOUR PARTICULAR CAR and if you have not yet invested in a SHOP MANUAL for the year make and model of you pride and joy muscle car your either not serious about your hobby, or most likely NOT A SERIOUS HOT RODDER! I constantly see guys SCREWING up installations, or adjustments,if you don,t know exactly what your doing, you need to either let the dealer do it and PRAY his mechanics are experianced and can read, OR..if your like ME, you would rather do it yourself and KNOW its been done correctly...
    if your not aware, heres where to order them....

    1-800-782-4356

    http://helminc.com/helm/homepage.asp?r=

    your average shop manual may cost $100-$150 ONCE! but youll easily save far more than that in reduced time and screw ups in under a years time or in many cases on one job vs having the dealer do the work!

    and yes old brittle electrical connectors can break, so they may need to be replaced, and while the search feature, is always an option here, on this site,
    too save time , look at the sub links in these threads, for links to connectors for repair work


    viewtopic.php?f=36&t=3105&p=8272&hilit=connectors+pigtails#p8272

    viewtopic.php?f=32&t=168&p=41767&hilit=connectors+pigtails#p41767
     
    Last edited by a moderator: Oct 1, 2017
  3. grumpyvette

    grumpyvette Administrator Staff Member

    other mods


    http://www.ws6.com/mycar.htm

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/

    http://www.thirdgen.org/newdesign/tech/tpimod1.shtml

    http://www.thirdgen.org/newdesign/tech/ ... pass.shtml

    http://www.thirdgen.org/newdesign/tech/ednitrous.shtml

    http://store.summitracing.com/default.a ... &x=23&y=12

    1985 vacuum line diagram
    [​IMG]


    [​IMG]

    http://www.thirdgen.org/tpimod2

    the above info should help, but get a SHOP MANUAL,TIMING LIGHT,VACUUM GAUGE,V.O.M. METER, YOULL NEED THEM,

    READ THIS SUB LINK
    viewtopic.php?f=32&t=168

    http://www.eficonnection.com/eficonnection/default.aspx

    [​IMG]
    [​IMG]

    How to Adjust your Early C4 TPS and Idle Speed -- 1 of 1


    Submitter's Name: Lars Grimsrud


    How to Adjust your Early C4 TPS and Idle Speed by Lars Grimsrud SVE Automotive Restoration Musclecar, Collector & Exotic Auto Repair & Restoration Broomfield, CO
    Rev. New 6-15-00
    This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle Position Switch (TPS) on the early C4 Corvette TPI systems.

    These steps apply specifically to the 1985 model year, and in general to other years. Later model years do not have adjustable TPS's. General Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed screw combined with a correct setting of the TPS.

    I've seen many of these cars that have had their idle speed corrected by well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways to make your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle Body (TB), disassemble it (it's incredibly easy, there are a total of about 5 pieces in it), clean the TB up really good with some spray carb cleaner, and put it back together.

    A nice clean TB will really put an edge on the performance improvement you will get by doing this procedure. The Service Manual has instructions for doing these operations, but the directions are scattered through several sections of the Manual.

    Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken directly from the Manual (all 3 different sections), and this process is absolutely correct.

    Tools & Equipment You will need the following tools and equipment:
    1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears.
    2. A good digital voltmeter that will read voltages less than 1 volt.
    3. A paper clip.
    4. A small screwdriver.


    Procedure
    There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC).

    Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.

    You will also be playing with the diagnostic connector under the dash. Remove the cover (if it's still in place). Bend your paper clip into a U shape. You will be playing with the two top right hand terminals (A and B) in the connector.
    1. First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It's located on the driver's side of the TB. Remove this plug if it's there.
    2. With the IAC connected and the ignition OFF, stick the paper clip into the diagnostic connector from A to B. This grounds the diagnostic lead.
    3. Turn the ignition to the ON position without starting the engine. Wait 30 seconds.
    4. Now, with the ignition still in the ON position, disconnect the IAC connector at the IAC.
    5. Remove the paper clip from the diagnostic connector.
    6. Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
    7. If your car is an automatic, set the parking brake and put the transmission in DRIVE. If your car is a manual, leave it in neutral. · Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
    8. Shut off the engine and re-connect the IAC. That's it for idle speed.

    Now on to the TPS.

    There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.

    1. Turn the ignition to the ON position without starting the engine.
    2. Loosen the TPS Torx adjustment screws. · Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
    3. Measure the voltage between the two top TPS wires.
    4. Adjust the TPS by rotating its position until you get a reading of .54 volts.
    5. Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
    6. Turn the ignition OFF. You are now in perfect adjustment on idle speed and TPS output.

    Start the engine. It may take a few seconds for the car to catch on to its new settings.

    ID adjust the TPS and IAC and idle screw and get it to run at 650 rpm, then throw in a can of both texico fuel injection cleaner and sea foam gas treatment, yes they do tend to clean up varnish and crud in the injectors, but in most cases its WATER in the fuel thats a more common problem than crud, if your changing fuel filters about every two years or more frequently

    http://www.thirdgen.org/tpimod2

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=3453&p=26193&hilit=vats#p26193

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=520&p=645&hilit=vats+resistor#p645

    http://forum.grumpysperformance.com/viewtopic.php?f=36&t=63&p=31920&hilit=starter+rebuild#p31920

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=5926&p=18562&hilit=starter+rebuild#p18562

    http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401

    reading thru these links, and sub links should give you a great deal of related info, if your having problems starting or getting your engine to run

    break down the problem in sections,
    will the engine spin over?
    does the starter work?
    is there fuel in the tank?
    is the fuel pump working?
    are you getting oil pressure?
    are you getting fuel pressure?
    do you have 13 volts at the battery?
    do you have voltage at the coil?
    spark at the plugs?
    are all the electrical connections good?
    are all the fuses good?
    get a code reader and a multi meter , pull codes check fuses and get a shop manual for your year corvette the auto parts store books leave out a great deal of info
     
  4. grumpyvette

    grumpyvette Administrator Staff Member

    cleaning your IAC, WARNING
    connecting your IAC to the cars wiring harness while its not properly installed in the throttle body, or trying to remove it with the wiring connected, will almost always result in almost certain over extension of the pintle and the components self destruction, it should be removed, cleaned carefully with throttle body cleaner spray(similar to carburetor cleaner spray), follow instructions below), after its cleaned and the throttle body is clean, re-install it into the throttle body BEFORE you connect it to the wiring harness

    BTW its located on the lower side of the throttle body


    http://www.ecklers.com/product.asp?pf_i ... pt_id=1279

    [​IMG]
    IDLE AIR CONTROL VALVE, located on lower pass side of THROTTLE BODY
    http://www.lbfun.com/warehouse/tech_inf ... 0Paper.pdf

    How to Adjust your Early C4 TPS and Idle Speed
    by Lars Grimsrud

    This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle
    Position Switch (TPS) on the early C4 Corvette TPI systems. These steps apply specifically to the 1985 model year, and in
    general to other years. Later model years do not have adjustable TPS’s.
    NOTE:
    The Minimum Idle Speed sequence outlined in this paper is taken directly from the 1985 and 1986 GM Corvette Service
    Manuals with some clarifications and simplifications added by me. Be aware that there are aftermarket manuals that outline a
    different sequence. I have used the sequence in this paper and verified that it is correct for the model years noted. You may
    choose to use the procedural sequence outlined and recommended by others.
    General
    Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed
    screw combined with a correct setting of the TPS. I’ve seen many of these cars that have had their idle speed “corrected” by
    well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up
    the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways to make
    your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle
    Body (TB), disassemble it (it’s incredible easy – there are a total of about 5 pieces in it…), clean the TB up really good with
    some spray carb cleaner, and put it back together. A nice clean TB will really put an edge on the performance improvement you
    will get by doing this procedure.
    NOTE: If you disassemble and clean your Throttle Body, including removal and cleaning of the IAC, it is recommended that
    you measure the extended length (protrusion) of the IAC “tip” before you re-install the IAC. If the “tip,” or “needle” of the IAC
    (referred to correctly as the “Pintle”), is extending out too far, you will jam it into the seat and damage it during re-installation.
    So before you install the IAC, measure the distance from the very tip of the Pintle to the surface of the IAC body that the gasket
    seats against (with the gasket removed). The distance should be 28mm (1-1/8”) or less. If the distance is greater than this, you
    must retract the Pintle into the IAC Body. There are two different styles of IACs:
    If your IAC has a “collar” around the electrical connector end, simply push on the Pintle with firm hand pressure while rocking it
    slightly side-to-side until it retracts.
    If your IAC does not have a “collar,” compress the Pintle Retaining Spring towards the body of the IAC and try turning the
    Pintle clockwise as seen from the Pintle end of the IAC. If it turns, keep turning until it retracts to the 28mm position. Then,
    return the spring to its original position, with the straight part of the spring end lined up with the flat surface under the Pintle
    head. If, however, the Pintle does not turn, use firm hand pressure as described above to retract it.
    Once set up, install the IAC with the gasket and torque to 13 ft-lbs.
    The Service Manual has instructions for doing the following operations, but the directions are scattered through several sections
    of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken
    directly from the Manual (all 3 different sections), and this process is absolutely correct.
    Tools & Equipment
    You will need the following tools and equipment:
    1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears.
    2. A good digital voltmeter that will read voltages less than 1 volt.
    3. A paper clip.
    4. A small screwdriver.
    Procedure
    There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC).
    Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.
    You will also be playing with the diagnostic connector under the dash. Remove the cover (if it’s still in place). Bend your paper
    clip into a “U” shape. You will be playing with the two top right hand terminals (“A” and “B”) in the connector.
    • First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered
    by a pressed-in plug. It’s located on the driver’s side of the TB. Remove this plug if it’s there.
    • With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.” This
    grounds the diagnostic lead.
    • Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds.
    • Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
    • Remove the paper clip from the diagnostic connector.
    • Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you
    may have to coax the engine a bit with the gas pedal to keep it running for a while.
    • If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in
    neutral.
    • Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
    • Shut off the engine and re-connect the IAC.
    NOTE: Some later year GM Shop Manuals recommend disconnecting the distributor ECM wire (“Timing Connector”) near the
    brake booster. This will prevent the ECM from altering timing – and idle rpm – during the rpm adjustment. Early GM Manuals
    do not contain this step. If you disconnect the timing connector, you will get a Code 42 stored in the memory of the ECM. The
    memory must be cleared of this code after re-connecting the timing connector.
    That’s it for idle speed. Now on to the TPS.
    There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires.
    You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of
    the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the
    connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.
    • Turn the ignition to the “ON” position without starting the engine.
    • Loosen the TPS Torx adjustment screws.
    • Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
    • Measure the voltage between the two top TPS wires.
    • Adjust the TPS by rotating its position until you get a reading of .54 volts.
    • Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
    • Turn the ignition “OFF.”
    You are now in perfect adjustment on idle speed and TPS output. Start the engine. It may take a few seconds for the car to
    “catch on” to its new settings.
    Questions, Comments & Technical Assistance
    If you have questions or comments regarding this article, or if you notice any errors that need to be corrected (which is quite
    possible since I’m writing this from memory…), please feel free to drop me an e-mail. Also, if you need any technical assistance
    or advice regarding this process, or other maintenance issues, feel free to contact me: V8FastCars@msn.com








     
    Last edited by a moderator: Sep 30, 2017
  5. grumpyvette

    grumpyvette Administrator Staff Member

    you can plug the rear fuel rail connection,remove the 9th cold start injector and plug the port it mounts to on the intake, it will result in it taking longer for the engine to start and on occasion a trouble code but no harm to the engine, BUT the smart route is to upgrade the CPU this eliminates the need for the 9th injector, speeds up the computer and makes the engine run better

    read this


    the original chip,transmitted at only 160 BAUD, :crazy:

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/870chart.pdf

    http://garage.grumpysperformance.com/index.php?threads/code-scanners-software.3096/#post-76215
    the ECM that came in 1986-1989 TPI Fbody's and Vettes is a series 1227165 (165). The ALDL data rate in this model can supply diagnostic data at 8192 BAUD.:thumbsup:

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/165chart.pdf

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/

    http://home.earthlink.net/~gellett/7165swap.htm

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/relay_harness.jpg

    http://www.eecis.udel.edu/~davis/z28/ECMs/85Fbody-wiring.pdf

    http://www.eecis.udel.edu/~davis/z28/ECMs/85-870v8MAF.jpg

    http://www.eecis.udel.edu/~davis/z28/ECMs/85_MAF_Burnoff.gif

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/ecms-photos1/ecm165memcalmod.jpg

    http://www.eecis.udel.edu/~davis/z28/ecm_swap/ecms-photos1/enginebayrelaymounts85.jpg

    viewtopic.php?f=32&t=168&p=202&hilit=+computer+1985#p202

    viewtopic.php?f=36&t=63&p=76&hilit=+computer+1985#p76
     
    Last edited by a moderator: Oct 8, 2018
  6. grumpyvette

    grumpyvette Administrator Staff Member

    VADER POSTED THIS INFO"


    There may be multiple problems, but the low idle RPM will affect the alternator output voltage as well as some of the other issues, so that would be among the first things to reconcile.

    Throttle Minimum Air Position

    Tools needed:
    1. Torx driver # T-20
    2. Paper Clip
    3. Small Punch
    4. Tachometer

    GENERAL NOTE: The engine should be at normal operating temperature before performing any adjustments. Never rely on the dash mounted instruments for diagnostics and adjustments. The oil pressure and temperature gauges and the voltmeter and tachometer just aren't calibrated accurately enough for diagnosis, but are a relative indication for monitoring the vehicle while driving.

    For this adjustment, the transmission will be in DRIVE while you're under the hood. You will need to securely set the parking brake and block the drive wheels. It would also be a good idea to have an assistant hold the service brake while you perform the adjustments.

    In order to successfully complete the adjustment, the IAC air passages and pintle need to be clean. The throttle plates and bores need to be clean as well. If this is not the case, you'll need to remove the air cleaner from TBI engines or the intake air bellows from TPI engines to gain access to the area to be cleaned. A spray-type carburetor cleaner works well for this. Cleaning the IAC passages on a TPI/MAF engine will set a DTC, but we'll be clearing that later. With the engine idling, direct the spray cleaner in to the IAC air passages and around the throttle plates. Shut off the engine and continue cleaning the throttle plates by opening the throttle manually. Once everything is satisfactorily cleaned, replace the air bellows on TPI engines. Many times, this alone can solve IAC/idle speed problems.

    If this doesn't solve the problem, you may need to remove and clean the IAC stepper motor. If the IAC appears to be clean and functioning properly, continue with the adjustment procedure.

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    Idle Air Control Cleaning

    You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

    Very little apparent varnish and dirt accumulation on the IAC pintle rack gear can cause poor or no operation. This is a comparison between a completely "dead" IAC and a completely funtional one, after cleaning:



    You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.



    Check the spring free length. Stretch the spring as necessary to get a minimum 2¼" free length. When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft, align the keyways with the keys molded into the IAC body, and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

    While the IAC is out, clean the air passages in the throttle body. The orifice in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush.

    When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    Locate the ALDL connector under the dash panel, in the driver's foot well area. Remove the plastic trim cover (if it is still there).



    Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets.



    Turn on the ignition, but don't start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. Under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector if your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

    Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400 RPM with the transmission in "DRIVE" on an automatic transmission car, 450 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

    Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.



    Throttle Position Sensor (TPS)

    Tools needed:
    1. Digital Volt-Ohm-Meter (VOM)
    2. Breakout jumper wires or probes (make your own)
    3. OPTION: AutoXray, Diacom, or similar scanner (will replace the VOM and jumper wires).

    Turn on ignition, but don't start the engine.

    With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.

    Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.

    With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)

    With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.

    Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.

    After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.

    Reinitializing the ECM

    If you set a DTC during the procedure, the SES light should be illuminated on the dash. This ECM retains DTC data for the previous 50 engine starts, so the codes will eventually be cleared. If you want more immediate results, after shutting down the engine disconnect the negative battery terminal for five minutes. This will clear the ECM of all diagnostic trouble codes. Clearing the ECM also clears any data learned about your engine, and clears the radio presets. If you have a Delco-Loc or Theft Loc II radio, make sure you follow the procedure to unlock the radio protection before disconnecting the battery. This five minutes is also just about long enough to clean both battery cables. Reconnect the battery. When you first start the engine after clearing the ECM, the engine will operate with base parameters programmed into the ECM PROM. These parameters may not be optimum for your engine, but the ECM will enter a Block Learn Mode soon after the engine is warm and enters Closed Loop Mode. The ECM will write new data tables specific to your engine and will eventually rely on those tables instead of the base tables of the factory program. You can expedite this process by driving the car for 20 minutes under varying conditions to allow the ECM to initialize. Or you can wait and drive the car normally at your convenience. The BLM tables are constantly being updated as sensor input ranges change, but the greatest change will occur within the first twenty minutes of Closed Loop operation."
     
  7. grumpyvette

    grumpyvette Administrator Staff Member

    http://www.ecklerscorvette.com/assets/p ... /A8906.pdf

    http://www.mamotorworks.com/corvette.ht ... t%20jumper

    high pressure air and some carb cleaner solvent can be very helpful cleaning out sticky or dirty parts
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]
    How to Adjust your Early C4 TPS and Idle Speed
    By Lars Grimsrud
    SVE Automotive Restoration
    Musclecar, Collector & Exotic Auto Repair & Restoration
    Broomfield, CO

    This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle Position Switch (TPS) on the early C4 Corvette TPI systems. These steps apply specifically to the 1985 model year, and it general to other years. Later models do not have adjustable TPS's.

    General:
    Idle speed and off-idle response on the early TPI systems is determined by correct adjustment of the minimum idle speed screw combined with a correct setting of the TPS. I've seen many of these cars that have had their idle speed "corrected" by well-intentioned mechanice and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways make your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle Body (TB), disassemble it (it's incredible easy - there are a total of about 5 pieces in it...), clean the TB up really good with some spray carb cleaner, and put it back together. A nice clean TB will really put an edge on the performance improvement you will get by doing this procedure.

    The Service Manual has instructions for doing these operations, but the directions are scattered through several sections of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken directly from the Manual (all 3 different sections), and this process is absolutely correct.

    Tools and Equipment
    You will need the following tools and equipment:
    1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears
    2. A good digital voltmeter that will read voltages less than 1 volt
    3. A paper clip
    4. A small screwdriver

    Procedure
    There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC. You will also be playing with the diagnostic connector under the dash. Remove the cover (if it’s still in place). Bend your paper clip into a “u” shape. You will be playing with the two top right hand terminals (“A” to “B”) in the connector.

    1. First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It’s located on the driver’s side of the TB. Remove this plug if it’s there.
    2. With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.” This grounds the diagnostic lead.
    3. Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds.
    4. Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
    5. Remove the paper clip from the diagnostic connector.
    6. Start the engine and allow it to reach normal operation temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
    7. If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in neutral.
    8. Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
    9. Shut off the engine and reconnect the IAC.

    That’s it for idle speed. Now on to the TPS.
    There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Min America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.

    1. Turn the ignition to the “ON” position without starting the engine.
    2. Loosen the TPS Torx adjustment screws.
    3. Set your volt meter to the low scale DC volt setting that will accurately read less than 1 volt.
    4. Measure the voltage between the two top TPS wires.
    5. Adjust the TPS by rotating its position until you get a reading of .54 volts.
    6. Tighten the Torx screws and recheck the voltage. Readjust if necessary to make sure voltage is right at .54
    7. Turn the ignition “OFF.”

    Addition by CorvetteForum Member Charles Warner

    As an addendum to “How to adjust your early C4 TPS and idle speed,” I would like to add that checking your WOT TPS voltage is also, potentially, a worthwhile endeavor. Frequently the TV cable that controls shifting pressure to the transmission binds the throttle linkage thereby not allowing for WOT. After measuring and, if necessary, adjustiong the idle voltage (nominally .54 volts) check the WOT voltage and ensure that approx. 4.5 volts is realized. A minimum of 4 volts at WOT are required for the ECM to go into fuel enrichment mode (FEM). If you are not seeing over 4 volts at WOT you are probably not opening the throttle to the stops and are not seeing FEM. A significant performanceimprovement is possible with this adjustment.
    Charles Warner
     
    Last edited by a moderator: Sep 11, 2016
  8. bytor

    bytor Well-Known Member

    Hey Grumpy, is it normal for the IAC on my 87 vette to make a clicking/buzz sound when turning the key on? I’m pretty sure the noise is coming from the IAC because when I disconnect it, the sound stops.
     
  9. grumpyvette

    grumpyvette Administrator Staff Member

    no! it sounds like its needs cleaning and its either broken or carboned up, but be aware that if you connect the IAC too the electrical harness wire while it is not installed in the throttle body housing and seated correctly and extended correctly it will self destruct as it over extends, or is manually compressed so read the directions on how its cleaned and re-installed

    Idle Air Control Cleaning
    You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.
    You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.
    When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.
    While the IAC is out, clean the air passages in the throttle body. The oriface in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush.
    When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.
     
  10. bytor

    bytor Well-Known Member

    Thanks Grumpy for the feedback. I was intending to pull the throttle body and give it a good cleaning anyway; I’ll check things out then.
    I found another minor issue with the fuel pump relay connector. I’m currently not experiencing any problems with the fuel pump relay but I noticed the wires going into relay connector are exposed a little bit. It looks like the insulation has shrunk and exposing about an 1/8 inch on a few of the wires. Here’s a picture below that shows what I’m talking about. I found this on the internet that shows the exposed wires. Mine is not this bad.



    What are my options for repairing this?

    Splice in a new connector pigtail like this.



    Or do they make repair kits for the connector that includes replacement terminals similar to this one?



    Any thoughts or other options?
     

    Attached Files:

  11. grumpyvette

    grumpyvette Administrator Staff Member

    on almost all older cars electrical connector pigtails and connectors for repairs are available, your local NAPA may have them listed and be able to provide many (AT EXORBITANT PRICING BUT OVER NIGHT DELIVERY) which on a connector that should cost $1-to-$2 each but from them, it may cost $7-to -$20 each yet may still be worth the cost at times, to get the car back in service

    viewtopic.php?f=36&t=3105&p=8272&hilit=connectors+pigtails#p8272

    if you shop around carefully its quite common to find you can purchase a dozen or a bag of 50 connectors for the price NAPA or advance auto charges for just a few connectors
    http://www.acdelcotechconnect.com/pi/wiring-connectors/gm/pigtails/

    http://www.ecklers.com/search.asp?actio ... chHistory=

    http://www.eficonnection.com/eficonnection/tpi_pigtails.aspx

    http://www.repairconnector.com/products ... 4-AWG.html

    http://www.acdelcotechconnect.com/pi/wi ... /pigtails/

    http://www.suresealconnections.com/

    http://www.garrettelec.com/kits/details ... NNWP25S617

    viewtopic.php?f=70&t=1443&p=28051&hilit=shrink#p28051

    http://www.repairconnector.com/

    http://www.waytekwire.com/automotive-connectors.htm

    http://www.rowand.net/Shop/Tech/Automot ... ectors.htm

    http://www.vette2vette.com/
     
  12. bytor

    bytor Well-Known Member

  13. Leoaln

    Leoaln New Member

    I read in the comment that there are 3 different IAC steppers and that they are not interchangeable. How do I determine which is the correct one that I need? 383 tpi setup in 1962 Willys, so I have no idea what model year it is from.
     
  14. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Look at the GM part number on the Throttle body.
    Should be there and Google identify the year.
     
  15. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    without pulling trouble codes and testing your simply guessing at best,
    break the issue down into separate issues,
    check ignition strength and timing,and voltage
    check fuel supply/delivery pressure and volume
    check cam timing and cylinder compression.
    check valve train control and valve adjustment
    check firing order and spark plug gap
    check the valve lift, and for work lobes
    check for vacuum leaks
    adjust your iac and tps
    check your exhaust back
    pressure
    verify sensors correct function
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    https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore,f,EAFeatured+Weight,f,Sale+Rank,f&q=zr13
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    [​IMG]
    all the answers are readily available, theres known testing procedures and listed test results you can expect, and procedures listed in the shop manual for isolating and testing components, you don,t need to be a genius, you just need to be logical and persistent and not afraid to learn new things while getting your hands dirty at times, don,t get overwhelmed , break everything down too easy individual problems and tests, verify and test all the sensors,and test for factors like consistent fuel pressure, known temps,expected voltage or ohms resistance, and vacuum readings and don,t randomly start replacing parts as that gets expensive and its rarely the most efficient way to eliminate problems(unless you get really lucky) with modern computer diagnostic software you,ll have some advantages but think logically, most automotive problems still concern, loose electrical connectors, defective sensors, lack of compression, fuel delivery issues ,fuel pressure, vacuum, temperature or electrical issues.

    http://www.helminc.com/helm

    [​IMG]


    the correct matching SHOP MANUAL
    TIMING LIGHT
    IR TEMP GUN
    VACUUM GAUGE
    MULTI METER
    FUEL PRESSURE GAUGE
    COMPRESSION TEST GAUGE

    keep in mind the basics you need to verify the fuel pressure is at about 40 psi if your dealing with a C4 corvette,
    you should NOT have significant exhaust back pressure, clogged catalytic converters,
    are a common problem on older c4 corvettes,

    verify the fuses are not blown, the trouble codes do not show any problems,
    all electrical grounds are reading good,
    verify theres at least 14.5 volts at the battery while its running, so you know the alternator functions,
    and all the injectors are functional with a noid light,
    all cylinders should read within 10% and show about 150 psi or greater.,
    on a compression test, verify the firing order,
    set the spark plug gaps at .045 ,
    and verify all the listed sensor values,
    verify the cam lobes are not worn, verify you have at least 10 psi of oil pressure per 1000 rpm.verify theres no vacuum leaks


    [​IMG]
    http://www.professionalequipment.com/ex ... ermometer/
    Wide temperature range from -58 to 1832°F (-50 to 1000°C)
    [​IMG]
    [​IMG]
    viewtopic.php?f=55&t=109
    [​IMG]
    [​IMG]
    you might have clogged catalytic converters, the ignition timing may be way off, you might have a worn out cam, the fuel pump may be defective, some injector(s) may be defective,check the alternator out-put check the fuel rail pressure use a noid light on the injector wiring, check the fuses,
    Ive found that the one most commonly over looked in my experience is that the stock exhaust system, is highly restrictive, especially if the catalytic converters are partly plugged and the stock fuel delivery system is not adequate,for the potential power, the heads and intake, allowable air flow potential, are all restrictive, and the stock cam timing and lift is already near max as it was designed to produce about 260 hp,and operate at under 5700 rpm, if you try too add an additional 100-200 hp, and 1000 rpm-2000 rpm to the engines power band, and too the engines output youll quickly find this to be a factor.
    I've also occasionally seen guys, improperly index or install a cam without degreeing it in correctly and thus have power band limitations.
    Id suggest you buy a factory shop manual, multi meter and a timing light, fuel pressure and vacuum gauge and start checking.:thumbsup:

    reading these links will be helpful
    yes I know it will take some time and effort to isolate and test
    but its the only 100% sure route to finding and fixing your problem,
    don,t get over whelmed,
    simply break the problem down to testing each basic sub system,
    test each related sensor and electrical component and electrical sensor and connection.
    some reading on the threads posted below, a bit of logic and deductive reasoning, and a multi meter and a shop manual will go a long way toward finding and fixing the problem.

    Measured Value
    Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
    Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
    Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
    Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
    MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
    Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
    MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
    Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
    TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

    Sensor Locations

    Sensor


    Location
    Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
    Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
    Oil Pressure Sender/Switch. Top, left hand rear of engine.
    Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
    MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
    Outside Temperature Sensor. Right side of engine, top right corner of radiator.
    In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
    MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
    Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
    TPS (Throttle Position Sensor). Right side of throttle body at the front.


    [​IMG]
    this is the most consistently accurate I.R temp gun I've used for testing[/img]
    [​IMG]
    http://www.testequipmentdepot.com/extech/thermometers-and-humidity-meters/infrared-thermometers/high-temperature-infrared-thermometer-58to1832f-50to1-laser-pointer-42545.htm?utm_source=bing&utm_medium=cpc&utm_campaign=NEXT - Bing Shopping - Extech&utm_term=1100200223789&utm_content=All Extech Products
    INFRARED TEMP GUN
    you always need a base line to start from, on a corvette.
    a logical step by step approach and keeping accurate notes helps.
    youll NEED a multi meter, a shop manual
    and a timing light and fuel pressure gauge at a minimum,
    set and verify your ignition timing, pull trouble codes,set your tps and iac,, then check for vacuum leaks on the lines and intake,then get out your multi meter and verify all the sensors, chances are good a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links. use of a shop manual and multi meter can be very helpful

    [​IMG]

    theres a vast amount of related data in the threads and sub-links,
    skipping those would be a huge waste of time
    (compared to reading through links,until you find the info you need)


    http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/


    http://garage.grumpysperformance.co...ng-high-flow-cats-on-exhaust.8401/#post-29318

    http://garage.grumpysperformance.co...s-cause-a-bad-idle-in-drive.14203/#post-72114

    http://garage.grumpysperformance.com/index.php?threads/testing-1985-89-m-a-f-sensor.1475/#post-43635

    http://garage.grumpysperformance.co...le-shooting-flow-chart-info.11536/#post-71845

    http://garage.grumpysperformance.co...ittent-cylinder-miss-problem.9478/#post-57225

    http://garage.grumpysperformance.co...g-your-tpi-maf-and-cpu-links.2825/#post-56790

    http://garage.grumpysperformance.co...-you-failed-emmision-testing.3522/#post-52999

    http://garage.grumpysperformance.co...and-verify-each-possibility.11219/#post-50643

    http://garage.grumpysperformance.co...-idles-and-sometimes-stalls.10688/#post-46303

    http://garage.grumpysperformance.com/index.php?threads/1991-c4-runs-like-crap.10616/#post-45635
     
    Last edited: Oct 9, 2018

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