I was coasting up to a stop light today with my foot off the gas and all of a sudden the car started increasing speed slightly on its own. I was watching the RPMs and they went up as the car was increasing speed then back down to normal then back up then back to normal. All of this was going on while I was coasting up to the stop light with my foot off the gas. I was like What the @#$%. Then when I stopped at the light while waiting for it to turn green with my foot on the brake the idle jumped up again about 500 RPM's over normal, held there for about 5 sec., then droped below normal to where the car almost stalled, then back up to normal. The has not done it since then. What could have caused the car to act up like this?? Could the Idle speed control motor be going bad??

Car is a 91 Camaro 305 TBI

 

If there's a lot of miles on the motor, the TPS may be failing.

 

is it tossing any codes?

 

no codes. When it started acting up I was waiting for the light to come on but never did. So the I should try replacing the TPS?? This is a none adjustable piece on my car correct??

 

Today the problem got really bad Idle went way up and stayed up. I think I found the problem though. I pulled the IAC valve out to check the pintle and orfice for any carbon buildup. While examining the pintle of the IAC I noticed that the pintle would not turn, I know it's suppose to for adjustment, so I left it because I didn't want to force it. I gave the pintle and shaft a light brushing with a brass brush to remove the carbon and while doing so the pintle seemed to loosen up. I lightly rotated the pintle back and forth and noticed that the pintle was starting to walk out, and knew this wasn't right, so I gently pulled on the end of the pintle and the whole thing came out. So I think that the pintle was sticking the whole time causeing poor idle. I'm going to go get a new IAC tomorrow from the dealer and hopefully I won't see the same problem again. Just one question. If I buy the IAC from the dealer will it come already preadjusted for my car or will I need to adjust it myself?? I know sometime when you buy these aftermarket your suppose to adjust them before putting them in, just wasn't sure if the same applied to Delco IAC's