1992 GMC Sierra idle is to high

1992 GMC SIERRA
185,000 MILES
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RAIDERROB
  • MEMBER
  • 3 POSTS
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.
Jul 18, 2013 at 9:23 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,246 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.
Jul 18, 2013 at 11:58 AM
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RAIDERROB
  • MEMBER
  • 3 POSTS
I changed the IAC and now the truck is idling higher? How would I check for vacuum leaks?
Aug 10, 2013 at 10:32 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,246 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.
Aug 10, 2013 at 12:19 PM
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