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87 1 ton Chevy, High idle problem

Discussion in 'Chevy Trucks' started by streetkit, Dec 13, 2001.

  1. streetkit

    streetkit Junior Member
    Messages: 15

    I have an 87 Chevy 1 ton crew cab 4x4 with a 350 TBI. It is idling quite high at about 1100 to 1200 RPM. What can be causing this? Also what are some of the symptoms of a bad fan clutch and also a clogged catalytic converter? Would either one of those possible problems contribute to a high idle? Any input would be greatly appreciated. Thanks.
  2. thelawnguy

    thelawnguy PlowSite.com Addict
    Messages: 1,011

    Check the TBI mounting gasket, if its leaking (and they are known to fail) they will cause a vacuum leak and high idle. Also check for vacuum leak from lines. Once you done those two things, if the idle is still high, remove the IAC from the TB (two wires coming from it, attached to the side or back of the TB with either two screws or a large 1 1/4 nut) and clean out the orifice with carb cleaner.

    A faulty temp sensor can cause the ECM to think the truck is always cold and cause the IAC to remain open longer than it should.

    Still have probs let me know I can copy the test procedure from the service manual for you (rather involved). But these are the most common causes of your problem.
  3. streetkit

    streetkit Junior Member
    Messages: 15

    Thanks Bill, I'll check the gasket and the TB ASAP. Pardon my ignorance but where would the temp sensor be located on this truck? (This is my first fuel injected rig)

    Any advise on identifying sumptoms of a clogged catalytic converter or a bad fan clutch?:confused:
  4. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    I'd bet on the bad gasket. Had one go out on our 89 305, idle just kept climbing as the leak got worse. Easy way to check is to spray carb cleaner around the base of the TBI housing and see if RPM changes.
  5. speedracer241

    speedracer241 Senior Member
    Messages: 325

    fan clutch

    most times the clutch will be loose. with the engine off check to see if it spins too freely, it should spin a little and stop. also move it foreward and back, there should be no movement that way. a bad converter will stink like rotten eggs and sound kinda plugged

    hope this helps
    Mark K
  6. streetkit

    streetkit Junior Member
    Messages: 15

    Hig idle problem

    OK, I was finally able to find some time to check for vacume leaks. Used some carb/throttle body cleaner and checked to see if rpm would go up at various locations but got nothing. Did get some bubbling in some spots where the intake manifold meets the heads. Could that be it?

    I also noticed that the throttle shaft on the throttle body doesn't always return to the "closed" idle position. It seems to stick whcih of course casues high idle. Pardon my ignorance, but are 87 throttle bodies supposed to have a return spring like a carb?:confused:

    There is no return spriong on this thing but it sure looks like there is a spot for one. Once again any ideas would be greatly appreciated.
  7. staley52

    staley52 Member
    from Iowa
    Messages: 98

    yes there should be a return spring