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1992 Cadillac Sedan Deville

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I was wonder if anyone else had this problem or similar problem with their 1992 Sedan Deville, Here goes, I have a rough idle, (not really a rough idle engine speeds up then slows down, sometimes dies) after engine has warmed up, after you have driven and then parked after engine has warmed up, when you start it back up engine runs fast then slow and somtimes dies if your just going along without pressing accelerator. After you have driven down the road say 100 feet this problem stops and car idles smooth until you shut it off again and the start it back up. I noticed that the idle speed controller motor cycles when it is doing this even with the engine off with the ignition on. What could be causing this? I am thinking it is an electrical problem, I check the error codes and it shows no error codes, on the Climate Control Panel, while doing the diagnostics check after the segment check. I recently had the car smogged last week and it passed with flying colors. In California, and you know how strict they are here on smog. I dont think its and engine problem it is some kind of problem with the ISC or the circuit that controls it.

Any information would be appreciated as how to fix this.


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I suggest checking the operation of the closed throttle switch on the ISC. Do a search in the archives on Idle Speed Control or ISC and read up. There is a method to verify the proper operation of the closed throttle switch via the climate control panel while in diagnostic mode.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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