Why does the idle speed motor screw on a 1989 Cadillac ElDorado sometimes vibrate immediately after turning off ignition?

Answer

It receives a barrage of messages from the computer and will twist and turn as it shuts the engine down. It controls, the idle according to the accelleration, ac use, alternator, emissions, etc. These are tricky little bastards, so if it's working ok, leave it alone. After a few years and two replacements, my 89 seville could never adjust it quite right. I tried everything. Used ones, new ones, smaller pins, the whole nine yards. They don't tell you this at CAdi, but when they go, the ISC modules pop up, pinning the accellerator, and scaring the crap out of you. Should it ever happen to you, brake as best you can, put it in park and turn off the engine. You'll see the pin fully extended on the end of the module. If you can't unscrew the pin (no pliers) break off the pin with a jack handle. You will idle really low and have to race it at the lights, but you'll get home without killing anyone. Think of all the gas you'll save, if you stall occasionally. Good luck

First answer by willie morris. Last edit by Trilo. Contributor trust: 103 [recommend contributor]. Question popularity: 52 [recommend question]