I have a '93 Corvette with the ZF trans. Just recently the idle jumped to about 1200 long after the car reaches operating temp. I did run a data log on the PCM and found what I thought were some interesting results. When I first start the car the idle is right around 660 and the TPS % is 0 with a voltage of 0.57. Shortly after driving the car, the TPS % and voltage start to rise, as does the RPM without applying any throttle. It seems to lock in at a TPS % of 1.2%, a voltage of 0.63, and a RPM of 1200. This leads me to believe the throttle is either not returning to its fully closed position or there is something wrong with the TPS. However if it's the throttle sticking, I don't understand why it's fine every time I first start the engine unless the ASR is somehow pulling on the throttle once the car is running for a bit.

Does anyone have any thoughts on where to look first? Am I on the right path or is the slight rise in TPS % and voltage inconsequential and the high idle is being caused by something else like a vacuum leak.

I really appreciate any advice you may offer. I did run into this same problem last year and I tried replacing the IAC, but that did not solve the problem. I don't really recall what solved it or whether it fixed itself.

Thanks,

Jim