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cold start idle hunt

Discussion in 'GM Powertrain' started by a.graham52, May 10, 2013.

  1. a.graham52

    a.graham52 Rockstar 100 Posts

    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?
  2. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    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.
  3. a.graham52

    a.graham52 Rockstar 100 Posts

    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. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    Propane (a torch) is a good tool to test for a leak in an intake manifold. Needless to say, use a little caution.
  5. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    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.
  6. a.graham52

    a.graham52 Rockstar 100 Posts

    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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