TPI minimum idle speed

G

george88gta

Active Member
Just finished going thru the ignition system. No more ignition noise on the radio. I installed a new coil, dist module and new wires. Engine is a TPI 350, 52mm throttle body, vortec heads, vortec/tpi intake base and SLP runners and a GM LT4 hot cam. ECM has been tuned for the mods. Next thing I want to tackle is the min idle speed. Shop manual states that it should be set at 450 rpm. Will this combo idle that slow? If not, what do you guys recommend for a min idle speed. One of the problems I was having is that when cruising, the car wil not go below 1000 rpm and the IAC count was at "0". Tuner states that engine should idle at 850 in gear.
 
Ive always tried to tune the TPI with a stock cam and stock torque converter, to about a 750rpm-800rpm idle in gear, as Ive found that to be the best compromise, if you set it lower than about 700rpm there tends to be a very slight hesitation if you floor the throttle that's not nearly as pronounced or noticeable just a few rpm higher, but get the rpms a bit higher and the car seems to jump when you put it in and out of gear requiring you to hold the brakes firmly, a basic P.I.T.A.
obviously if your chasing a vacuum leak, or your ignition timing is not correctly set or if you've got injector or fuel supply issues your beating a dead horse untill those issues are addressed first
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.


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Interesting. I had it set to 650, in neutral, and it wouldnt idle down when cruising. Will experiment today and post results.
 
Played around with this a bit today. First thing I ran in to was that my old reliable dwell tach reads about 150 - 200 rpm less than my scanner. The scanner and dash tach were close so I retired the dwell tach. I followed the procedure, as outlined in the GM shop manual, and I could get the engine to idle around 500 rpm. Removed all test equipment, cleared the set timing error code and started the engine. Idle was terrible, surging about 200+/- rpm. Went for a ride to let ECM relearn the car. No real change in the idle. Timing is dead on at 8 degrees and the TPS was at 0.54 volts, key on engine off and measured with the scanner. Fuel pressure is at 44 psi. Fuel filter is about 3 months old, fuel is 92 octane Shell. Attached the scanner and IAC count was "0" and engine was idling somewhere around 800 rpm in neutral. As an experiment, I started turning in the idle adjustment screw and engine smoothed out at about 950 rpm. ECM is calling for desired idle at 900 rpm. Dont have a helper available, to ride the brakes, so trying your method ( in gear and set to 800 rpm) is a bit dicey. Ran out of time, will play with this one again. For now, it is running decent.
 
let us know how it works out and what you find during the process, keep in mind that the stock converter speeds vary a bit and if your is tighter than average it tends to jump into gear from idle while a looser converter doesn,t exhibit that tendency to nearly the same degree

read these threads

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http://www.aa1car.com/library/2003/us60324.htm
 
Probably should have mentioned I have a TCI 2500 stall converter installed. Made a big difference, car doesnt try to drive thru the brakes anymore, when stopped at a light, etc..
 
OK, latest update on this. I went back thru the system, looking for vacuum leaks and couldnt find any. Next thing I did was to replace the plug wires, dist module and the coil. Slight improvement. Went back to my logbook and the only thing I never changed was the ECM chip/module. My upgrade to the ECM works with the stock module and a Hypertech module. I had a Hypertech module in the shop so I figured " why not?". Replaced the module, took the old girl out for a nice long ride ( over an hour) and she is happier than I can remember. Still cruises about 1000 - 1100 rpm, no throttle, but idles down to around 800 at a stop light. Idle is a bit rough, but I feel that is the cam. I believe the correct statement here is " quit while you are ahead". Plan now is to enjoy the rest of the summer cruising.
 
as long as YOUR happy, with the results and it runs decent your doing fine! glad everything's worked out
 
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