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idle too high

Discussion in 'The Garage' started by jacksprat1599, Dec 17, 2003.

  1. jacksprat1599

    jacksprat1599 Registered Member

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    Hi,I am a new member and just purchased an 89 4x4 suburban with a 350 that has 154k on the odo.It is idling way too fast after it is warm.I haven't touched a thing,there is no check engine light and the vacum lines look good.Anyone have any ideas?
     
  2. MilpitasK5

    MilpitasK5 1/2 ton status

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    Try and see if the throttle return spring is bad or getting hung up.
    Good luck.
     
  3. BigOrange90Jimmy

    BigOrange90Jimmy 1/2 ton status Premium Member

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    You might have a small air leak in the throttle body somewhere. Mine had that same problem when I first got it. I don't know where it was coming from though.
     
  4. jacksprat1599

    jacksprat1599 Registered Member

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    How did you fix the small air leak and where excactly was it located. and the throttle linkage is just fine
     
  5. heavy4x4

    heavy4x4 1/2 ton status

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    Does it idle high all the time or just after it reaches operating temperature? First thing I'd replace is the coolant temperature sensor next to the thermostat housing...that tells the ecm what temp the engine is running at, and if it's not working right, it might be telling the computer the engine is too cold, thus the computer says to dump more fuel in for a higher idle to raise the temp. Give that a try...$5 sensor, and it should fix it. /forums/images/graemlins/thumb.gif
     
  6. jacksprat1599

    jacksprat1599 Registered Member

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    Idles high only after reaching op temp.It idles fast enough to require more brake pedal than I would like to use.I'm worried about the old tranny building up too much heat at lights.
     
  7. heavy4x4

    heavy4x4 1/2 ton status

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    Any "throttle leak" to speak of on these vehicles is air getting between the tbi unit (carb) and intake manifold past the gasket. Take off the aircleaner assembly, then you'll see 3 bolts. Don't just tighten them to make any leak go away...you'll probably strip something out and have a bigger problem. Get a new gasket, unbolt the 3 bolts, lift the tbi unit up (don't need to disconnect fuel lines or anything) and put the new gasket in place of the old...bolt back down. Usually when this part leaks, either 1) you can hear it if you get your head in there or 2) it's not enough of a leak to bump idle up much (only sensor past that point that would have any effect is the oxygen sensor in the exhaust manifold).
     
  8. heavy4x4

    heavy4x4 1/2 ton status

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    [ QUOTE ]
    Idles high only after reaching op temp.It idles fast enough to require more brake pedal than I would like to use.I'm worried about the old tranny building up too much heat at lights.

    [/ QUOTE ]

    Yes, fix the problem...otherwise you will burn up your torque convertor. /forums/images/graemlins/eek.gif

    P.S. Welcome to CK5. /forums/images/graemlins/thumb.gif
     
  9. jacksprat1599

    jacksprat1599 Registered Member

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    Thanks for the info and the welcome.Any other areas I should check out on this vintage and mileage.I've only had it 2 days and I forgot to mention it is a 1/2 ton.
     
  10. skratch

    skratch 1/2 ton status

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    I've got the same problem with my 87. I have replaced every single sensor on the engine, all the vaccum lines, resealed the TBI unit to the intake, rebuilt the TBI, new springs . . . And it still idles to high. IT blew the output from my tranny and the input for my transfer the first time and now it has blown the sun gear case in my 700!
    I need to figure this out before it blows my new tranny too.

    If I'm hearing this right there could be a leak in the body og the TBI itself!?
    How in the world would I go about finding that and fixing it?

    Welcome to the club jack. /forums/images/graemlins/thumb.gif
    Maybe we can figure this one out together.
     
  11. jacksprat1599

    jacksprat1599 Registered Member

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    Hey ,
    I figured out my high idle problem and it ain't good.All the sensors and vacum lines are fine.It is leaking engine vacum because of a burnt and stuck open exhaust valve.It will cost about a thousand to fix,hope that's not whats wrong with your 87.
     
  12. 99firehawk

    99firehawk 1/2 ton status

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    1000 for a valve job????????????? I wish I was your mechanic.
     
  13. fwdjunky

    fwdjunky 1/2 ton status

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    There is an air bleed valve inside the throttle body that controls idle speed. I believe its adjustable (sorry, I'm at work and don't have "the book" with me and I can't remember the exact name) and have heard it can start to leak by on high milage engines. Wish I could be more specific for you, but it might be something to look at. Chilton has a very good book on early chevy fuel injection systems that gives the specifics on this. The one in my local library is covered with my greasy finger prints. Good luck and welcome to the show.
     
  14. skratch

    skratch 1/2 ton status

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    That sounds like it might be something for me to look into.

    I doubt it's a valve on my engine since I put a new long block in a few years ago, but you never know.
     
  15. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    base plate gasket on the throttle body is famouns for failing. I just replaced the one on my 88 454 Burb for the exact same problem.

    Get some carb cleaner and spray the base of the throttle body and see if the idle changes.
     
  16. skratch

    skratch 1/2 ton status

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    I'll have to try that too.
    I wouldn't at all be suprised, even though I did put in new gaskets awhile back. I just pulled my throttle body spacer to help too. It really didn't do that much for the truck in the first place and even with the spacers for the throttle cable and TV bracket it still wasn't working all right.

    Grim where u live in Atlanta, my brother is down in Fayetteville, and we visit him quite a bit, I'd love to meet you next time were in the area. /forums/images/graemlins/thumb.gif
     

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