I have an intermittent high idle problem. Sometimes the car idles at 1200 rpms in gear while stopped. And sometimes after doing a quick wot throttle snap it idles back down. It doesn't work all the time. What could cause this? a tps going bad?

Checked my tps voltage. 0.463 volts closed, and 4.63 at wot. I slowly checked the voltage from closed throttle to open and I get a smooth increase in voltage.

I replaced the IAC, the engine didn't idle high as much as it used too. But 3 different times it was idling at 1200 rpms again in gear. Now I have no idea what could be causing this.

 

Just went through this with mine. I was sure it HAD to be an EFI problem so I went through all the normal steps-cleaned the throttle body and blades, cleaned the IAC and it's bore, changed the IAC, reset the TPS, reset the base idle-and it still did it-randomly. It did it one day while I was messing with it with the hood up and I saw that the throttle wasn't returning to the stop. The throttle return spring was worn out, and you can't change it. I went to the hardware store and got a supplemental throttle return spring to go from the throttle lever on the TB to the throttle cable bracket and it hasn't done it since.