Last night I decided to remove and clean the IAC because I had noticed an occasional surge in the idle (very slight but I like everything to be perfect). I cleaned the pintle and the spring with throttle body cleaner and reinstalled it. I started he car up and it idled around 1500 rpm. I shut the car off and went to adjust the idle. I set it at about 550 rpm following the procedure in my Haynes manual. I checked my TPS voltage and it had dropped down to .40 When I went to adjust it, I couldn't get it to go any higher than .48 because there was no more room for adjustment. There has to be something wrong with that picture. I ended up adjusting the idle screw so it would idle about 700 and the highest I could get the TPS was .50 I started the car up and drove around a bit and stopped at the gas station. When I started the car back up, it was idling real erradically and was trying to stall. I revved the motor a few times and that seemed to smooth it out. I was able to drive home. When I started it up again at home, the car stumbled for a couple seconds and then died. Tried it again 3 times and it did the same thing. I started it again and immediately revved it for a few seconds and the idle came back down around 800 and satyed there. I messed with the idle adjustments and TPS voltage a little more but with no luck so I went to bed. When i went to start the car this morning, it did the same thing. It would die almost immediately. If I revved it and held it at about 1000-1500 rpm for 10 seconds or so, it would drop back and idle fine. But once I turned the car off and started it again it would do the same thing. The computer is not throwing any codes and the car runs great other than that. I'm thinking I could've cooked the IAC somehow or maybe I just need to clean it better. When I get home, I will clean out the IAC passages in the throttle body really well and see if that helps. Any other suggestions? Would the low TPS voltage cause this? Sorry for the long post but I really need to get this fixed ASAP.

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1991 Z28 - 350 TPI, T56, McLeod street clutch, LT4 pressure plate, Pro 5.0 shifter, ported plenum & runners, AFPR, Hooker shorty headers w/o AIR, Flowmaster muffler, homeade ram-air, SSM subframe connectors, Kenny Brown STB, Global West steering box brace, Steve Spohn adjustable torque arm and T56 crossmember

 

when u remove the IAC motor, there is a procedure that you have to go through to reset it, otherwise it will not function correctly, im not sure wut it is, but i'll try to find it. at least im pretty sure about that.

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88' GTA 350 MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass

 

It just involves turning the car on and back off again. It *should* reset itself.

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

I find it better to jump the A and B terminals on the ALDL to ensure the IAC fully exends with the key on...then I remove the jumper, start the car then shut it off..start it again and go for a drive.I bring it up to 45 mph or so a few times and it always seems to work best for my cars.
IAC works great after.

 

Ok I fixed the problem. All I did was manually push the pintle all the way back into the housing and then installed it. I followed the standard procedure for resetting the IAC and it works fine now. The TPS is still slightly off. I cna only get it to read .51 volts and then it runs out of room for adjustment. Thanks for all the help.

 

I didnt think the 90-92 sd cars TPS was adjustable? I know you can open the holes up. But.. I thought that where ever you set the idle speed, the computer would take that as closed throttle. Then Tps would stay show around .71 volts.

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

I havn't heard this about the speed/density cars until today and I've heard a couple people say the same thing so I guess it's probably be true. It definitely makes sense. I'll check the TPS when I get home again. Maybe it reset itself. Thanks for the help guys. Should it be at .54 or .71 volts?

 

The voltage won't change, its a potentiometer who's voltage output is dependent on its resistance. The ECM will "self zero" and assume that the TPS voltage with the throttle blades closed is 0%. Keep in mind, I don't mean having 2 volts with the throttle blades closed will zero the ECM!

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-Jason M. 1991 Camaro Z28