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high idle..what else besides throttle body gasket

Discussion in 'GM Powertrain' started by Big6ft6, Aug 20, 2007.

  1. Big6ft6

    Big6ft6 Rockstar 100 Posts

    I started by 89 suburban (350) after is sat for a week and it is idling very high probably 2500+rpm (don't have a tach). Never has this before

    popping the gas doesn't bring it down. A vacuum leak would make it idle rough, not high, right?

    I haven't had time to check much, but any other things I should check besides vacuum leaks?

    Any ideas would be great thanks.
  2. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    Test for a leak

    I wouldn't rule out vacuum leaks. Get out the carb cleaner and spray it around the base of the carb/throttle body and at the intake manifold gasket areas. Some prefer to use propane for this test. I like to take the air cleaner off and cup my hands over the air intake. If as I progressively choke off the airflow the idle normalizes, a vacuum leak is indicated.
    1 person likes this.
  3. racer14

    racer14 New Member

    The idle air control motor could be stuck or the passage could be contaminated. To check, pull the air cleaner assy off, and look at the passenger rear of the throttle body. You'll see a 4-wire square plug sticking out at a 45 degree angle, and a hole inside the throat of the body in that corner. If you plug that hole with your finger, the truck should die. If not, a vacuum leak is your issue.
    1 person likes this.
  4. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Thanks Racer!

    I was wondering where the IAC valve is on these throttle bodies. I will check when I get home. The contamination might be possible becuase I had the air cleaner off while the truck was sitting before this high-idle started.

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