I have a 1989 L98 IROC that is having Hi idle problems. I have read through the FORUM and have checked and or replaced the typical Items that is associated with Hi idle problems....(Looks to be a very common problem)...... I made a home made smoke machine to find any and all vacuum leak(s)... I did find and correct a couple small vacuum leaks........(passenger side valve cover gasket and an unpluged vacuum port just below butterflys on the bottom of throttle body)........ I smoke tested again and the only place I could see smoke leaking out was by the springs on the side of the throttle body. Fixing the other vaccum leaks idle did drop a bit.. My question is has anyone else had this problem and could a leak on the butterfly shaft cause such hi idle speed 1200-1500 RPM.

Absolutely, I keep telling people not to forget to check the shaft, especially on stock throttle bodies. I had a Holley I had to rebuild once also. Kept getting a code 33 MAF because of it too.

This is why you shouldn't grab that can of throttle body cleaner and go spraying it all over the insides of the throttle body. It can wash out the shaft lube that GM (Rochester) put there to help prevent throttle shaft wear.

Spray some water around the throttle shaft with the engine running. If you hear a slurpy sucking sound, its time to get the throttle shaft bushings done.

I was having the same problem. I opted to have mine rebuilt rather than go with an aftermarket TB. I used these guys to rebuild mine. It was probably a 2 week turn-around with shipping. Maybe less if you are on the West Coast. No more irritating idle surge.

http://docinjector.com/default.htm

I am waiting for a rebuilt one that I got off of Ebay. I hope this will solve my high idle problem(s) Should be here Sat.



http://www.ebay.com/itm/TPI-52mm-bored-rebuilt-throttle-body-1985-88-tuned-port-Camaro-Firebird-Corvette-/162042327006?hash=item25ba79afde

Let us know the results after you put the rebuilt one on the car.

I'm guessing there is no way the shafts can be 100% tight...correct? Is there an acceptable amount that the IAC can compensate for? I had mine rebuilt awhile back and never did a smoke check on it until today. Just for kicks I took the hose of the brake booster and had a friend who was visiting (who vapes) blow a vape cloud into the hose-intake. I see the vapor coming out of the shaft on both sides of the TB. But I'm not sure how to tell if any should escape or if there is an acceptable amount.

Thoughts?

Well, that's a good question. I'm not sure as to how much vapor could escape. Usually you can feel excessive play. I guess i would run the motor and spray the shaft ends and see if there was a change in idle. But i like the idea of the E vape. I know some people who vape, and the look like they are on fire when they take a drag off them things.

Well, it ended up being a combination of things. The replacement throttle body helped allot but did not completely solve the problem. I also replaced the ECM and now idle is good. Now just getting code 21, but running great.

I forgot to mention. I did go ahead and put an unlit propane torch up to the shaft ends while the car was running. That yielded no change in the idle speed. So I guess a little blow by on the TB shaft is acceptable.