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  1. #1
    Jr. Engineer
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    Default cold start idle hunt

    i have a 2002 gmc sierra with a 4.3L 5spd. on some cold mornings ill start it from a cold soak over night and the idle will hunt quite a bit. go from 900 to 300 and back and forth over and over for about 15 seconds or so. thing sounds like its cammed up. i cannot find any vacuum leaks and sprayed the intake with carb cleaner. i had this happen in my 93 w/305 and it was the ignition module in the dizzy. but this doenst have that correct? anyone got any ideas?
    "i dont think you got the picture. i got a beautiful picture. this baby happens to have an extra turn of speed, which is the only thing i care about. you dont understnad what happens do you? they make cars. they make 'em exactly the same way. one or two of 'em turn out to be something special. nobody knows why. i know why. i may be kiddin' myself, but i think i can make somethin' out of that sad little bucket of bolts." ~ Tennessee Steinmetz

  2. #2

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    Not sure about the 4.3, but some GM engines will act like that if the throttle body is dirty.

    You've looked for a vacuum leak, probably checked the hoses; did you consider the intake manifold gasket. A leak there would act like (because it is) a vacuum leak.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  3. #3
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    Default

    The tb is clean, and I sprayed around the intake with carb cleaner and no leak appeared. The only thing I haven't got a possitive idea of is the back of the block. I'll have to look at that tomorrow.

  4. #4

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    Quote Originally Posted by a.graham52 View Post
    and I sprayed around the intake with carb cleaner and no leak appeared.
    Propane (a torch) is a good tool to test for a leak in an intake manifold. Needless to say, use a little caution.

  5. #5
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    You could possibly have a leak at the MAP sensor, It is located between the firewall and the back of the intake manifold. It is a plastic sensor, BUT it has a rubber seal on the nipple that sticks into the manifold. On my truck that seal ripped, and was letting excess air in. This is a huge problem, as this will effect the A/F ratio and make it run erratic.
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  6. #6
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    Default

    ill check it out. i think i found the problem though. i removed the IAC and cleaned/lubed it and stuck it back in. havnt had any issues in 4 days.

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