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Q: Bad idling after coolant temp sensor replacement

asked by on July 05, 2016

Hi my truck has had a bad coolant temp sensor for 7-8 months well I finally got around to replacing it and warm engine starts have been so much smoother and the temperature gauge works again. Well now the engine doesn't seem to want to idle sometimes it will idle very very low almost to the point it stalls I'm thinking possibly a vacuum leak that was covered up by the bad coolant temp sensor causing the engine to rich but I would like to hear what a professional has to say thanks! Also the truck has a bad knock sensor but I don't think that would have anything to do with it.

My car has 240000 miles.
My car has an automatic transmission.

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If you have a bad knock sensor, then the engine timing may be going too low and causing the low rough idle. If the scanner gives a code, then have it diagnosed and fixed. A vacuum leak will also cause the rough idle and I recommend having this checked for, located, and diagnosed.

GMC
Idling
2003
V8-6.0L
timing
running rough
Sierra 2500 HD
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