I've got an 89 IROC-Z w/ a 305 TPI. When I first start it up the idle is a little high, about 1400, but after driving a minute or two it pulls itself down the street. I have to ride the brake on residential streets. When I shift back to park it revs up to about 3500rpm.
I also had a bad mass air sensor that was triggering the engine light, and replaced it. Also replaced the TPS and IAC to attempt to fix idle problem. The mechanic set up minimum idle on it and set the voltage. It started doing it again on the way home from the shop. The next day I adjusted the position of the TPS myself, it idled great, drove great (fantastic, was the only time I'd ever driven her w/o high idle), but would occasionally buck and stall in traffic or green light starts and the engine light would intermittently come on. So I brought it back and he reset tps and minimum idle. No servicelight or stalling but back to same problem. He's a good mechanic but mainly works on newer cars so maybe we're missing something obvious.
Some extra info for troubleshooting... fuel pump was recently replaced, no vacuum leaks heard/seen under the hood (i do have one leak under the dash, a/c vent related), throttle linkage not too tight, return spring works fine, i cleaned butterfly valves and checked that they close tight.
Any input would be helpful as my next step is to take it to a high end chevy shop and open my wallet, and then have to explain more money being spent on my "girlfriend". I hope I'm just missing something obvious.

 

jaredamos,

That's a tough one. It's been a few years since my car had TPI, so I'm trying to recall some of the troubleshooting I did when I had a similar problem...

If your car still has EGR, you may want to look at the EGR valve & solenoid. The EGR valve is primarily a controlled vacuum leak but, if it's malfunctioning, it can cause all kinds of trouble (see the many posts regarding EGR).

Also, if you smell gas when it sputters/dies, you may have bad fuel injectors. I had this happen years ago... car ran fine until it got hot and I went to stoplights... then it would sputter and sometimes die. Eventually the bad injector(s) stuck open and hydrolocked the engine. An easy check to make sure they're ELECTRICALLY fine, is to unplug the electrical connector and check the resistance of each injector with an ohm gauge. They should all be pretty close to each other. I'm not sure how you would check them to make sure they're mechanically working ok without pulling them and sending them to a specialty shop.

I hope this helps. Best of luck!

 

Thanks for the help. I will check out the EGR. I'll check posts for best way to check it. I know the injectors were all replaced before I bought it. Maybe something with the installation?
I'm also wondering if it could be getting air from the vacuum leak under the dash? I don't know much about the vacuum lines for the a/c controls but the hiss comes from behind the passenger side dash underside and the vents will switch off when accelerating.
My other theory is improper TPS setup. This is because when I adjusted it, minimum to mininum, it ran awesome, but would act up in traffic. But I didn't set th voltage after moving the sensor. Maybe I need to adjust the position of the TPS and then reset the voltage with it in the new desired position. I didn't know how to set the voltage and wasn't comfortable doing it, that's why I had him set it up. Does that make sense though?

 

A vacuum leak can definitely effect idle quality. I would fix the leak and then see if there's an improvement. If its not better, I would check that EGR valve and/or solenoid.

Again, I'm going from memory, but...

I believe I would set the IAC (using the instructions on this site), and adjust my idle via the throttle blade stop screw (if needed). Once I had the idle the way I want it, I would then loosen the screws on the TPS and adjust it between .54 (stock) and .60 volts, and tighten the screws back up. Then, turn the car off, plug everything back in, disconnect the battery for a few minutes, reconnect it, and take it for a test drive. All this allows you to set the minimum air and the idle speed/position.

 

thanks, i'll post on how it goes.

 

well, finally got time to work on it. Set IAC and TPS.TPS was a little high. Was at .61. Set to .54 now. Ran great on first two drives. It would actually slow down when you let off the gas. Then it started back again. Gonna bring it to Chevy shop when I can. Seems too much for my skills (moderate) and free time(virtually nonexistent).
I've got no engine light on and it is running great, just high idle. Maybe I'll drive it some more, give computer more time to adjust. Just wish i had time..... frustrating.

 

ok ya'll, sorry for the delay. Got mycar back from Vern's Chevy Center. Problem was identified and minimized. I'll explain. Hope this helps anyone with similar issue.
The high idle was caused by a worn throttle body. The steel shaft had worn out the aluminum and causd there to be a lot of play in the throttle. Vern reset minimum air best as could be done. Idle is much better, not quite perfect. But at least now i press the gas when driving instead of riding the break. Only way to truly fix it is to replace throttle body (300-400$). I think that will be my Christmas present.
Thanks for the help and advice. And I would definitely recommend Vern's Chevy Shop to anyone in the Clearwater, FL area. This guy knows Chevys (and Pontiacs).

 

I'm having a similar problem, and I also traced it back to my throttle body. I just ordered a refurb off ebay, so we'll see how it goes. In my situation, one off my TPS bolts broke off and I bad to drill it out. I retapped it and upsized the bolt. Everything was matched but for whatever reason, I'm getting a vacuum leak around that new bolt. I've tried everything to seal it, and well, it's time to replace it.

If this doesn't work, I'm giong to drive it into the lake and see how that goes!

Ken