More problems from my 86...

T

tehcarguy

Member
Well, I finally got her running, but now there's some new problems. The car will start fine when it's cold. It will idle around 6-800 rpm. When it gets up to temp, I will stop at a light and it will be idling at 10-1100 rpm. When coming down my driveway, I have to stay on the brakes or it will accelerate. When I put it in park, it will rev up to 15-1800 rpm and stay there and won't go down. I've cleaned the throttle body, and replaced the IAC, and it is still doing this. The throttle lever isn't getting stuck. I have no idea what else to check.
 
I adjusted the TPS, it was at only .41 volts and it drives alot better now. However, the problem of the high idling in drive still persists when it's warm. It still revs high and won't go down when I put it in park, but it's intermittent. I cleaned the throttle body, and bought a new IAC about a week ago. It's not giving me any codes either. Someone told me there was a recall or something on the PROMs in 86, could that be related? Also, when I cleaned the throttle body I did not reset the comp by unplugging the battery when I unplugged the MAF. Could this also be causing the problems?
 
Its a whole lot easier to track down the problem if the cars in front of you, than guessing about stuff from posted info,concentrate on verifying your sensors are functioning correctly and possible vacuum leaks,verify your oil and coolant levels,verify your running at least 13.5 volts at idle, with a multi meter, and check for timing issues as a first step
naturally you-ll want to verify each sensors working and that your ignition timings correct as a first step, but I also generally look for leaking vacuum hoses, bad o2 sensors, fuel pressure issues, and I always suggest adjusting the valves at idle once the engines up to temp.

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Something is causing the throttle arm to get stuck slightly open. I just did a test with all the cables (throttle cable. cruise, etc.) disconnected from the throttle arm, revved the car and it's still getting stuck. I lubricated the Shaft inside the TB, and everywhere else, still getting stuck. I have no idea what's causing this.
 
Id suggest temporarily removing the throttle body for a close visual inspection, and use of a new gasket when its re-installed and careful cleaning and verifying the throttle linkage and TV cable, to the transmission has a bit of slack or at least no significant tension, then reset the iac and tps
stuff like this is usually easy to diagnose when your on-site but a total P.I.T.A. over the internet,unfortunately


THIS WAS POSTED SEVERAL PLACES ON THE INTERNET


http://books.google.com/books?id=1Ti3kH ... dy&f=false


Throttle Body Cleaning 101

Throttle Body maintenance 101: READ THESE INSTRUCTIONS ENTIRELY BEFORE STARTING THIS PROJECT! (YOU WILL NEED A DIGITAL MULTIMETER IF YOU TAKE THE TPS OFF! DON'T ATTEMPT TO REMOVE THE TPS IF YOU DON'T HAVE ONE, IT IS MANDATORY!) You should also buy the gasket kit from GM that includes the 4 gaskets and costs about $25. Using your screwdriver remove the air duct in front of the throttle body, now open the throttle by hand (engine off of course) and feel behind the throttle blades. Did your fingers go all black and gungy (yucky isn\'t it). You need to get that throttle body off and scrub it cleaner than clean can be. Preparation: Go and buy some throttle body cleaner (NOT CARBURETOR CLEANER), and buy yourself a new toothbrush, your old one just got a new life. Get an old bowl or something similar, rags and perhaps some of those lovely rubber surgical gloves. Getting right on in there remove the 3 pin connector from the throttle position sensor, and remove all the pipe work going to the throttle body, there is a little water spillage, not much. Also remove the IAC connector (a 4 wire square connector) it\'s a bit fiddly to get to. Now the tricky part, the throttle cables need to be released, (manual and auto cars are different), the cables are fixed with wonderful things called Jesus clips, you slide a screwdriver under it and ping it disappears, you mutter \'Jesus where did that go\' - what a name for an item. Best to cover the area with a cloth to capture any pinging that goes on. With the cables released the throttle body should be free to remove. Undo the four long bolts holding it to the plenum, careful when prizing it apart, do not damage the gasket unless you are replacing it. Now you thought you were clear didn\'t you, nope, GM put a little booby trap underneath. There is a small vacuum tube with a rubber elbow that needs to be pulled off, be careful with this hose, they tend to get brittle and break with age. You\'re free! Now comes the really dirty part. Put the throttle body in the bowl and spray with throttle body cleaner and scrub like crazy, especially around the throttle blades. Its great, really messy but the final spray just cleans it all off and there you have a gleaming throttle body. Now using a 30-32mm spanner remove the IAC valve (that\'s the large black looking thing on the side), mind the gasket. Clean the spring and pintle and if you can get inside the orifice and clean the seat area. Make sure that the small hole going from the throttle mouth to the IAC is clear. Finally just spray the spring and pintle with WD40 and replace the IAC valve. Final check - and perhaps another blast with the cleaner to remove any surface muck still there. You may want to soak a rag with throttle body cleaner and clean as far in the plenum as you can get. Allow to dry and replace the throttle body on the plenum, taking great care with the gasket ensure it is positioned correctly. Ensure all the connectors cables and pipes are back on (don\'t forget the little tube underneath). This may be a good point to check and adjust your throttle position sensor. Get two paper clips, straighten out and slide into the end of the TPS sensor connector, A (earth) and B (tps output), keep the wires separate and turn the ignition on (car off) and measure the voltage at the wires and adjust by loosening the torx bolts, if necessary, to 0.54 volts - this is the normal idle setting. Self satisfaction. Job done now you should start your Corvette and stand back to admire the even tickover and you will marvel at the smooth response the car now seems to have. If nothing else you have pampered and tinkered for about an hour, got filthy, therefore justifying your time and got a tangible result afterwards, all that remains to do is test drive the car to the nearest (or in fact not so nearest pub). Congratulate yourself with a beer and apply wide beaming grin. "
 

hey grumpy?
I can,t get my 1986 corvette to idles smooth at 650 rpm, any suggestions


the first thing Id point out is that it will really idle best if set to a minimum of 750-800rpm if its stock, any lower will tend to have issues.
did you verify TDC and set the timing per the fsm?

have you verified the ignition advance curve?

did you adjust the valves at idle ?


honestly I see so many guys skip checking the basics or assuming that the fuel pressure, valve adjustment is correct or that the fuel pressure regulator and vacuum lines are good and the ignition wire plugs, cap rotor, and wires etc. are fine that its no wonder they have issues locating the problem source
i had a guy in the shop a while back with a similar issue, he had owned a 1985 vette for 14 years and never changed the cap rotor or plug wires and acted shocked when i pulled the cap and about 80% of the cap and rotor were powdered crud and the distributor was a pile of rust flakes internally, he had never changed them in 14 years, nor had he adjusted the valves, and pulling the valve covers told me oil changes were also a rare occurance.

cars require maintenance and semi regular adjustments to run correctly

you will be amazed at what you can learn reading the links and sub-links rather than skipping reading thru them

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