I have been having problems with my cars idle for a while now, today I finally buckled down and a friend and I set the minimum idle and the TPS voltage. The car was idling rock steady at 500rpm with the IAC unplugged (yes we hooked up the ALDL connector and ran hte IAC all the way in). I plugged up the IAC and took the car for a ride and now the problems with my idle are worse than before! The car will sit at 650rpm then drop down to 300 or 400 rpm; almost stall out, and jump back up to 650. It will do this over and over and finally leveled out at 650rpm. What's driving me nuts is it's dropping well below the set minimum idle position, what the heck can this be! I've already changed the ignition module, coil, esc module, and the IAC is new, BUT it came from a 1991 Camaro TBI engine (please tell me these are the same!?). Thanks in advance for any help guys.

 

could be the IAC from the TBI i would think that they would be diff, since most of the TBI and TPI stuff is completely different not to mention a whole diff intake system, ur best bet is to replace with a new stock replacement IAC for your car. also when u do it to clean all the crap outa the TB, get a wire brush and some tube cleaner brushes and get all in that thing to get all that carbon and crap out and use intake cleaner thats safe for teflon. also make sure u adjust the IAC stem to be the right amount etc as stated in the manual.

your not throwing any codes are u?

 

No codes, TB is clean; what's driving me insane is that it's going BELOW minimum idle. I have a GM stock IAC sitting here that I'm going to swap. It seems to me like the damn IAC turned OUT entirely instead of in when we put the car in diagnostic mode. Maybe the IAC has it's terminals turned around for the TBI? Or perhaps a model year change? I know the TPS is backwards for some vehicles but I don't know about the IAC.

 

yea i would replace it anyways with a NEW stock replacement, dont mess with used stuff. they are cheap i thought. i wouldnt ever swap out non TPI parts on a TPI these intakes are weird and dont like parts that arent designed for them.

 

Part is the identical part number, I've been told it's identical. ECM has the proper idle set, I know because I set it when I burned the prom. I'm going to swap in the used GM IAC I have and if that doesn't fix it I'm going to lose my mind! I know the car can idle just fine, I just had it doing it with that IAC unplugged. I'm going to strip it this weekend, clean the TB like there's no tommorow, plug in the new IAC reset the ECM, and see how it reacts.

 

i had a problem like this, turned out 5/8 injectors were bad. had them replaced and idle was fixed

 

on how many injectors can your car operate on? on a v8 in paticular? supposed to be all 8 but if some go bad what happens?