[chphlds]

my car runs fine on the highway ,but at idle it races up sometimes,and then slows back to almost stalling.any help would be much appreciated

[Ruthlessmr]

could be a vacuum leak
spray around the hoses with carb cleaner you will hear it change if you find the leak

[T-bucket23]

Originally Posted by chphlds

my car runs fine on the highway ,but at idle it races up sometimes,and then slows back to almost stalling.any help would be much appreciated

Idle air control stuck

[chphlds]

thanks for the info guys.checked for vacume leaks and found none,and set the iac to specs but still having problem.was told by previous owner that it needs to be pluged into the obi and a disc put into lap top to tune the tpi. does this sound right?

[LATECH]

Sorta. GM has an updated PROM (programmed Read Only emory) chip for that car. I would bet there is an updated one you can install for a surge or rolling Idle. They used to cost 45 bucks. It installes inside the ECM . Not sure if one is still available for your IROC. Go to see the general (General motors) at least they may be able to help you.
You can erase it with ultraviolet light , but retuning it may prove to be tedious.
It will have some numbers and letters on it. That tells the calibration, from there the GM counterguy, if he is worth his salt can look to see if it has been upgraded. ( I would bet money that it has.)
Howell engine development has them for about 250 bucks.

[chphlds]

thanks for the info.the dealer was my next step,but just trying to avoid the cost. thanks again

[LATECH]

Bofore you go for a new prom, check the number on the one installed as of now, so you have something to throw at the counterman when you go into the dealer.
AND, before that, be sure about vacuum leaks/unmetered air.
Many times a vacuum leak was the issue. The upper intake to lower intake seemed to be plagued by this. New gaskets would usually cure it.
Be certain the PCV system is working and the valve shuttles properly
Check the EGR, take it off and clean it , to be sure it seals.
Clean the throttle body and the IAC pintle and seat.
Did you perorm a minimum air rate adjust ment?
Last but not least is the MAF.. Be careful with that one. Take it off, clean with a dedicated MAF sensor cleaner ONLY. I sometimes very softly use a Q Tip to clean the thermistors inside as they get blanketed with media from the paper air filter.
It is a very very good idea, after cleaning a MAF to wait about 15 minutes before plugging it in, especially on one of those old "hotwire" sensors. If not it can damage the internal circuitry from excess current flow through it to heat the wire.
If you have done all these things.....then off to the chebby dealer
Oh one other thing. If you have an OBD1 scanner you should check the data stream to be sure the O2 sensor isnt causing the system to run lean, or drop in and out of closed loop at Idle speed.O2 sensors are a maintenace item , like a spark plug. Maybe try that first if it looks original. It may help.

[AutoGear]

I had this same problem in my Trans Am. I had already changed all my vacuum hoses, checked the O2 sensor, Had taken the upper intake off to clean it (mouse nest) as well so it had new gaskets; I also had rebuilt the distributor. I still had an idle drop out issue at random. The only constant was that IF it was going to have an idle drop out issue, it was apparent as soon as I started the car; it wouldn't just pop up if I had driven the car for an hour. I took it to a garage that had a guy who was a GM wrench back in the 80s and is familiar with this setup. He cleaned the IAC, checked the MAF, cleaned it; checked the data stream for the O2 sensor, checked the PCV setup, and all accessible gakets. And we replaced the TPS with a Delco unit he had on the shelf. It was the computer, but I got one from the local junkyard for $35 and we swapped it out to test. Rather than trust a used one from a car with no windows that sat in the rain; I got one from TPIParts.net

[chphlds]

will try all that then if no sucess,off to the dealer.thanks for your help guys.it is appreciated