I first got the car this past spring, the weather was warm and I noticed no problem. The idle was always around 1k in park and 900 in gear, I suppose this is normal. When the weather got cooler it would go to 1500 on cold start and settle down after a few minutes. Once the weather got cold it would not settle down until I started driving. Being fuel injected I know you should not have to tap the pedal to get the idle to settle down, but finally I tried it and it worked but only after warming up a little. And thats where I'm at right now. I'm thinking it is a sensor but not sure which one, no idiot lights are on at the moment. Thanks for any help you may be able to offer.

Greg

Welcome to GM Forum!

Coolant temperature affects the idle speed. Based on the tables I've seen (which vary by engine, and sometimes by year), the fastest the engine will idle is 1600 RPM, but that'* at well below freezing. Once the engine'* been running for a couple minutes, the coolant will warm up and the idle speed will drop.

If the idle is any higher, or if the car dies when your foot comes off the gas pedal, you'll need to replace your IAC valve. <$20 at RockAuto.

How does your temp gauge read? Does it seem to be reading about the right temp? When up to temp it should read around 190* to 200* If the gauge is reading lower then that, then your ECT sensor is bad, and that will cause the idle to run to high.

Also keep in mind that GM is notorious for their "Less than accurate" instrumentation. Tachometers are usually a generalization, serving as a needle to tell you the difference between imminent destruction and idle.

Your IAC may very well need to be cleaned as well too.

The usual first steps to take on this kind of issue are if possible to scan the tps sensor. The next step would be to clean the TB by removing it and doing a thorough cleaning. While doing those double check for major vacuum leaks that may cause the high idle. Then go after the IAC.

I was in single digit temps and the idle never went above 1600 and does not stall when my foot is off the gas, lately the idle will stay high even when the temp comes up to operating range unless I tap the gas pedal or put it in gear

Coolant temp reads normal, the idle stays high even after temp comes up to operating range unless I tap the gas pedal or put it in gear

All the instruments seem to be reading fairly accurate, the worst is the fuel gauge, I can go about 100 miles after the needle reads empty and of course no idiot light

What is the procedure for scanning the TPS, I do not have a scan tool but I do have a DMM, no check engine light is on at the moment. I had thought about cleaning the TB but wanted to make sure there was not something else that may be causing this. The idle is stable around 1k in park and 900 in gear once warmed up and driven or kicked down, (I know I should not have to do this but it works)

This write up will explain how to test it.

https://www.gmforum.com/trouble-shooting-test-procedures-141/testing-tps-throttle-position-sensor-279319/