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Mysterious Rough Idle

Discussion in 'GM Powertrain' started by tnvolsone, Sep 10, 2007.

  1. tnvolsone

    tnvolsone New Member

    Hey all I'm having a real issue with a new truck that I just got it's a 92 1500 2WD with 30000 on the motor (GM crate) I'm an experienced mechanic having been one professionally for over 13 years. Well now the intro is done here is the problem. I'm having an idle problem after the vehicle reaches operating temp. it feels like it is missing and starving for fuel. I checked the fuel pressure its fine I sprayed carb cleaner all around to check for vacuum leaks there were none. I checked the cap, rotor, wires, and plugs ( They all needed replaced) I replaced them all with Delco stuff (of course) I was having an IAC issue after I hooked up to the scanner so I replaced the carboned up one, I did have a code 42 talking about the ESC not sure on the diagnosis of this particular item if anyone has had this type of issue any help would be appreciated I'm not one to just hang parts and see if that fixes it.
    Thanks in advance.
    S
  2. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    Air leak

    Sounds like you done your homework. As you know rough idle often points to an air leak. I'd start chasing an air leak, either a vacuum leak or a metered-air leak (between the MAF sensor and the throttle body.) I first try to confirm the air leak then isolate it. To test for an air leak I cup my hands over the air intake gradually increasing how much I cover the inlet. If the idle smooths out, I know I have a leak. Then I proceed to locate it either with carb cleaner or propane. (Use caution when using flameables around a running engine)
    If you don't confirm an air leak it is back to square one.
  3. Toymyster

    Toymyster Rockstar 100 Posts

    Sounds like you have all your bases covered!!! Have you checked you coolant temp sensor?? Or patterned the TPS?? How about your pick-up coil and ignition module?? Based on what you have said, you've already checked everything I would, so now I'm just throwing ideas out!! How is your fuel filter?? Were the 92s TBI or port injected?? I forgot!! Sometimes on TBIs, the throttle shaft wears out and creates a small vacuum leak.
    Good hunting!!
  4. joker23

    joker23 New Member

    I'm not sure about your particular motor, but I've found that this is a common issue with newer Tahoe's and Subs due to build up in the throttle body around the butterfly. I wiped mine down with a rag and she started running like a champ. I was thinking it was some sort of failure and it ended up being the simplest thing it could have been. As it turns out, this is the same thing the local dealership does for their "throttle body service".
  5. big red

    big red Member

    it could be the dist. pick-up. could be getting hot and lossing its magnetic properties somewhat thus killing the engine.

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