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my 91 deville has had a complete ignition tune up ...and injectors cleaned. once it gets warmed up it has a rough idle and will die at stop lights. it runs fine until I take my foot off the gas
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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my 91 deville has had a complete ignition tune up ...and injectors cleaned. once it gets warmed up it has a rough idle and will die at stop lights. it runs fine until I take my foot off the gas
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sounds like a problem with the ISC - Idle Speed Control motor -
either unplugged or just plain dead -
 

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Discussion Starter #3
ill check it out thanks ...also there are no diagnostic codes that come up.

another thing I would like to mention is that the previous owner said he never put anything but regular (87 octane) gasoline. any thoughts on that?
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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The 4.9 has no knock sensor, thus it was designed to run on premium. I tried 87 on mine years ago and had detonation. I went back to 92. I never tried 89, but it might work. If you are hearing detonation, move up one grade and try that. If you still hear detonation, go to the factory recommended 92.

That said, octane has absolutely no affect on your stalling problem, if that is what you where getting at.
 

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Discussion Starter #5
thank you ...yes were working on fixing the stalling issue. the isc motor is next on our list ...ill post here what we find out ...much appreciated!
 

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thank you ...yes were working on fixing the stalling issue. the isc motor is next on our list ...ill post here what we find out ...much appreciated!
tested the ipc motor ...no problems with it. any other suggestions? we'll need all the help we can get with this!
 

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White Diamond '03 DHS (with DTS floor shift)
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How did you test the ISC motor?
When you turn the key on, does it engage the throttle arm and hold the throttle open just slightly?
 
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