Cadillac Repair: Frequent but not constant High Idle Speed, speed bill, scan tool

Question
Bill,

This problem is driving me nuts!
I have a 1992 Deville with 120K on it. It runs and looks beautiful with the exception of this frequent high idle speed that is  much like being on cruise control.
Recently, an inner fuse was replaced that kept the transmission from shifting out of first gear. This was done after being told I needed a new transmission. That problem is now cured.

Is it related? Any ideas? Someone said something about an "idle motor." Does that sound right? Is it very expensive?

Your help would be gratefully accepted!!!

Beryl

Answer
Hi Beryl, There is a long procedure for checking timing and all the adjustments to the idle speed, tps and isc motor. Then the computor needs to be relearned and that can take care of a high idle provided a sensor isn't out of adjustment or bad. If the battery was disconnected then the idle will need to be relearned or a higher idle can result. Just replaceing the isc motor might cure your problem but for $150 plus labor I would want to be sure and have it checked out first. The trans and idle problem could be related if the battery was disconnected. It would be best to have someone look at the car because it could be something simple that hooking up a scan tool might find. Bill