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  1. #1

    Default Basic troubleshooting for a slight rough idle

    I'm attempting to not start throwing parts at this thing. Here's the rundown:
    99 k1500, 136k miles - slight stumble at idle. NO CEL codes.
    New fuel/air filters. Plugs have about 40k on them. Wires are original.

    Am I correct in assuming that problems with EGR and Idle valves, temp sensor and misfires will show up in a CEL? I sure would like to think its vacuum related but haven't found a leak as of yet and its only a minor stumble. She seems to accelerate smoothly. The idle problem seems to have come on all of a sudden and not progressed - but I could be wrong.

    Anyone offer a list of possible culprits?
    Thanks
    maury

  2. #2

    Default

    Could be dirty injectors. You might try running some seafoam through the gas tank. I do that ocassionally and it seems to run smoother once I have finished that tank and put fresh gas in.
    Gary

    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

  3. #3

    Default

    Gary,

    Forgot to mention I did seafoam the truck just recently with no difference. I try to keep techron in the tank every 4-5 fillups. I had the injectors in my old bimmer (with over 200k) professionally cleaned and balanced. There was moderate improvement but not as much as I would have thought at that mileage. I guess without any codes to work with, I'm at the mercy of changing parts. I'll start with the least $$ first.

  4. #4

    Default

    Could it be the Idle Air Control Valve?
    It wouldn't cost more than a possible new o-ring to tidy up and have the computer reset the IACV pintle position.
    Are we having fun, yet?

  5. #5

    Default

    Is the fuel pressure up to spec and steady?
    '98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
    '92 Ford Explorer XLT 4x4 4.0 L A4LD BW13-54 Trac-loc rear
    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  6. #6

    Default

    Fuel pressure is within specs. New pump/sending unit assembly and filter. I changed the pump assembly because the gas gauge was possessed. The IACV is something I have to investigate. Anyone have a link to info on this?

  7. #7

    Default

    .........and would a bad IACV throw a code? I understand it wouldn't if its only the o-ring.

  8. #8

    Default

    try cleaning your idle air sensor..that worked for me..

  9. #9
    Jr. Apprentice Kaedenman's Avatar
    Join Date
    Dec 2007
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    Great White North
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    Default

    I had/have a slight rough ile too. Mine is a 2008, though. They said they found the problem to be a bad 02 sensor. After they changed it, I still notice a slightly rough idle when stopped in drive. My other non GM vehicles never did this.

  10. #10
    Jr. Apprentice bkovacs's Avatar
    Join Date
    May 2008
    Location
    Cleveland Ohio
    Posts
    25

    Default

    Quote Originally Posted by Kaedenman View Post
    I had/have a slight rough ile too. Mine is a 2008, though. They said they found the problem to be a bad 02 sensor. After they changed it, I still notice a slightly rough idle when stopped in drive. My other non GM vehicles never did this.
    if it was the 02 sensor, it would probably throw a code, I would say change your wires! if they are orginal, how about cap and rotor? that would usually cause problems throughout the rpm range though not just at idle, IAC could be the problem
    '99 K2500 Suburban Vortec 7400
    '00 k2500 Silverado Vortec 6000 ex. cab

    '84 K5 Blazer 4x4 lifted (defunct)
    '86 Dodge w250 4x4 lifted (also defunct)

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