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Edward
Edward, Service Technician
Category: Car
Satisfied Customers: 2276
Experience:  20 + years experience on various makes and models.
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Cadillac STS: I have a 94 Cadillac STS

Resolved Question:

I have a 94 Cadillac STS That ran perfect before I had the Torque converter replaced - now it starts up at 750 rpm or at 2200 rpm - my mechanic found a bad timing sensor and that did nothing - the car is drivable buy the throttle revs up at any time - if it starts up at 2200 rpm, tapping on the gas pedal several times will bring the rpm's back down - we're at a loss - the car gave me 16-18 mph in town and 32+ on highway by keeping speed under 65 mph - there are no new codes and we've been over this engine with a fine toothed comb
Submitted: 1 year ago.
Category: Car
Expert:  Edward replied 1 year ago.
Hello, my name is XXXXX XXXXX I will try to help with your question, For the engine to crank up and hang at 2200 rpms, it is definitely getting too much air to idle that high at times anyway. Here are a couple of things I would do and I believe it will solve your problem.

1. I would make sure the throttle cable and linkage isn't binding, Go out under the hood and have somebody push the gas pedal and let off a good 5 or 6 times, make sure the throttle returns all the way to the stop everytime, and lubricate the linkage on the throttle body to make sure it's not hanging up anywhere.

2. Get a can of carb cleaner and an old toothbrush, Take the fresh air hose off the throttle body, spray the carb cleaner and scrub any dirt and varnish out of the throttle body, pay close attention to where the butterfly swivels in the throttle body and get all the varnish out from the inside of the throttle body,

3. Make sure the cruise control servo isn't binding as well. and isn't trying to pull the throttle plate open at idle.

4. After cleaning the throttle body, disconnect both positive and negative cables from the battery for a few minutes, then physically touch the pos. and neg. cable together for about 30 seconds, this should reset the adaptives in the Engine Control Module. and allow the adaptive idle speed to reset.

If none of the above helps, then I would suspect a failed or sticking Idle Speed Control Motor. Pull it out and luck at the plunger, if it looks damage or is original, then I would certainly try another one. Here is a picture of the component.

graphic
Customer: replied 1 year ago.

Thanks for the reply - I didn't know how much I could write in the box when asking a question so here's some more infor - the idle can go up at any time - sitting in the driveway start up the car running normal and wham - it revs up - linkage is free nothing appears to be pulling in - just idle raises up -you can be driving along and pull up to a stop sign - driving normal then hit the next stop and wham up again doesn't do it all the time very erratic does this help in any way we've looked at the items you mentioned and looked for other codes nothing appears out of the ordinary car drives fine no hesitation or sputter just very unreliable at this point

Expert:  Edward replied 1 year ago.
That is interesting, only thing that can make it idle that fast, is air. So it's getting too much air at idle when that happens. The Idle Speed Control Motor basically bypasses air around the throttle plate. So basically it's just an air measuring device controlled by the ECM. If there was a vacuum leak big enough to cause that type of idle problem, then I feel sure the check engine light would go off and you would have lean codes stored. If you've already cleaned the throttle body and looked at what I've previously mentioned, then I would certainly try another Idle Speed Control Motor, as it is the component that controls air around the throttle plate. FYI, I have also had an engine idle up like yours at times, and when it idles up, smack the side of the Idle Speed Control Motor with a screwdriver handle and jar it around a little. if the idle falls right when you smack it, that's a good sign the motor has failed.
Edward, Service Technician
Category: Car
Satisfied Customers: 2276
Experience: 20 + years experience on various makes and models.
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