Rough idle with check engine light after warming up on cold days

Tiny
GRIFFINLOGAN
  • MEMBER
  • 1994 GMC SIERRA
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 133,000 MILES
Hey there. I own the truck listed above it is a 2500 with the 350 engine. I often start the truck up in the mornings for about five to ten minutes when the temperature is usually minus ten degrees Celsius. It runs fine until I start driving. Then the check engine light turns on and it surges when it idles a swell as when I stop while the truck is in drive. Loss of power when the rpm is low as well. Once I start it later in the afternoon the truck is fine. I am by no means a mechanic and have no idea what this would be. Hoping to hear back soon and I love my truck and would like it running 100% again. Thanks
Tuesday, October 24th, 2017 AT 3:07 PM

3 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
The "check engine" light is an indicator for a system that monitors many electronic functions in the system, also called the "malfunction indicator lamp" (MIL). It can come on for any of hundreds of different causes from any of the systems that the computer monitors. Some are very important and can lead to further component or engine damage and some are emissions related not as serious but still a problem and need to be repaired.

Your first step is to have the computer scanned to retrieve the trouble codes that were set when the check engine light came on. Those codes will give you specific information about what the computer saw and will get you pointed in the right direction to find your problem.

On your vehicle you can jump A and B of the diagnostic connector and the CEL with flash codes numbers in the form of flashes.
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Tuesday, October 24th, 2017 AT 5:11 PM
Tiny
GRIFFINLOGAN
  • MEMBER
  • 2 POSTS
The check engine light sometimes does not come on when it idles rough. But I find it only idles rough when in gear in both D and R. Could it maybe be a vacuum or choke? Usually only occurs when it is cold out. As of right now there is no check engine light but surges while in gear only when it is colder outside. Thanks
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Tuesday, October 24th, 2017 AT 6:23 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
You need to get the codes read before concluding anything. Your truck does not even have a choke. It is fuel injected.
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Tuesday, October 24th, 2017 AT 6:26 PM

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