Are you getting any codes? Maybe a high idle speed code? As said above, it may be your IAC motor (assuming your throttle body is stock, and your motor is still stock). I was having a similar issue to yours with my '98, intermittent high idle with an otherwise stock car, and no other effect to driveability other than idle speed. The only DTC I ever got was just a high idle speed code one time.

I was able to hear the IAC motor grinding when I'd turn the key off. It had to be real quiet around the car and the hood needed to be up for me to hear it. No need to start the car, just park in the garage or someplace real quiet (maybe at night) and turn the key to the 'run' position, wait a second, then turn it off. Have the hood popped and stand outside the driver's door (just operate the key through the open window). Listen for a grinding, or 'rocks in a can' sound coming from the TB right after you turn the key off. If you hear that, I'd try replacing the IAC motor. All my issues (both high idle and grinding noise) went away with the new IAC.

The IAC motor is on the left (driver's) upper side of the throttle body. On that left side you will find two items attched to the throttle body (IAC motor and Throttle Position Sensor). The upper attachment is the IAC motor, it's directly above the TPS. The IAC motor has one eletrical connection (plugs in) and is held in with two torx bits. It's very easy to remove/replace, but after you loosen and remove the torx bits, don't worry if you have to pull on the unit a little to get it out, there is a rubber o-ring that seals it into place that may stick a little.

I think a new IAC is about $100 from the dealers. Maybe closer to $150.

Hope that helps.

 

Sure did fix it.

 

Great! I knew it would. Did ya get your moneys worth?

 

From you? Definitely!