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1992 GMC Sierra idle is to high

Tiny
RAIDERROB
  • MEMBER
  • 1992 GMC SIERRA
  • 185,000 MILES
When starting truck idle is high after a few minuets idle goes down to 1500 rpms in neutral after driving when stopped in gear idle goes down to 1000 rpms. Just changed spark plugs and no improvement on idle rpms.
Thursday, July 18th, 2013 AT 4:23 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Check for engine vacuum leaks and check the idle air control valve (IAC). The IAC is located on the throttle body and is an electric solenoid that is responsible for maintaining the engine's idle.
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Thursday, July 18th, 2013 AT 6:58 PM
Tiny
RAIDERROB
  • MEMBER
  • 3 POSTS
I changed the IAC and now the truck is idling higher? How would I check for vacuum leaks?
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Saturday, August 10th, 2013 AT 5:32 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Most techs will use carb cleaner and spray it around the vacuum hoses and intake. If the engine RPM's increase, there is a leak. Please be careful, however. Remember that carb cleaner is flammable.
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Saturday, August 10th, 2013 AT 7:19 PM

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