I need help, I now have a 89 GTA with almost 71,000 miles. Now the bad since 08 it has only went about 700 miles. The car has a idle issue, it likes to idle around 1350 then sometimes around 1000 and sometimes around 650. When the car is not idling right there is a loss of power. I've had 3 different shops look at it and they all say the same thing, Per the scanners they are using there is nothing wrong. Everything reads correct except for the high idle. The car has new injectors, distributor and TPS installed by the PO. I have installed new IAC and temp sensor along with a T-stat since there wasn't one. Also have done plugs and wire's. It did go through PA inspection running like this and I do drive it everyday. I have checked for vacuum leaks and have found none. I am a bit old school and know only enough about TPI to get me in trouble.

 

Might be that the throttle blades are sticking in throttle body on a random basis. The shaft can wear out in there and cause this problem. Bascially, it would be a mechanical problem. It is often over looked because we instantly think it must be a computer problem.

Try swapping out our Throttle body with a know good one.

 

If the blades were sticking, then the throttle would not be against the stop right? I have checked this when it idles high and it is against the stop.

 

Sexy. I have an '88 with 63k on it that just got a nice new drivetrain. Looks like new again, just like yours. Amazing how far a sandblasting cabinet and some paint go in the midst of an engine swap.

Look into setting your minimum idle air rate. This should involve grounding the ALDL connector, waiting 30 seconds, unplugging the IAC, pulling the ground from the ALDL, starting the engine and manually adjusting the throttle blades to the correct RPM. This will be in gear with a helper on the brakes and preferably with the rear on jackstands with the ebrake pulled tight. Then shut down, plug in the IAC and reset the ECM. After this you will probably need to adjust the TPS and maybe the timing if it was far out but that should get you pretty close. Just dont blip the throttle during adjustment.

I've seen idle specs for 305 and 350 TPI's as low as 450 RPM, though I always shoot for 600-650 on stock engines. Some engines seem happy that low in gear, some dont.