93 cutlass 3.1 odd idle problems

For the past month I have been having a come and go high idle problem. No real pattern . Just decides it wants to high idle. Sometimes when I start it after a 2 mile drive sometime when I put it in park after a 15 mile ride. Goes away after a few days sometimes. But it always comes back. Start high idle at like 1200 and goes steady to about 2k. Drive Idle at stop 800-1k. I noticed when it down shifts when it hits 1k during a downshift it will spike to 1200 and just before it stops in motion it will spike 1200 again. Otherwise drives fine. Any tips or clues would be a great help. Thanks.

I had the same problem with my 94 3.1. It turned out to be the IAC. Check the resistance between the pins on the IAC motor. A-B & C-D should be 20-40 ohms. When I replaced mine I had to drive around for a while to get the ECM to learn it's new idle. You might want to clean out the trottle body while your at it.