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Thread: rough idle

  1. #1

    Default rough idle

    i have a 93 z71 with a 350. I was driving one day and it has a really rough idle and almost stalls. so i changed the spark plugs and noticed the driver side was running rich and the passanger side was running lean. What would cause this? I also changed the plug wire,cap and rotor but did not help. any suggestions??

  2. #2
    Legend cascott325's Avatar
    Join Date
    Aug 2008
    Lawrenceburg, Kentucky


    fuel pressure, misfire, timing?
    2000 silverado with a 5.3l v8, shorty headers, upgraded plugs, 10 mil wires, magnaflow high flow cats, flowmaster 80 series muffler(2 in 2 out) w/ 18 inch stainless silverline tips. i have a k&n CIA. its a 4x4 z71 offroad package. Ls model.
    extended cab 160k miles, truxedo low profile bed cover, diablo sport predator tuner.
    reman tranny @ 130k miles

  3. #3


    its is misfiring. I havent checked the fuel pressure yet. it stops misfiring when i am going 70 mph.

  4. #4


    Exhaust leak causing the comp to dump more fuel?

  5. #5
    Jr. Mechanic
    Join Date
    Jul 2008
    Bluegrass Country


    When you say the left side is running lean, does it have a crust build up on the electrode? These trucks have a history with the intake gaskets, especially on the left side. Have you had to add coolant recently? If so, instead of a fuel related problem, you may have an intake gasket leaking fouling the plugs. Just a hint, I've replaced dozens of those gaskets for the same reason, rough idle, miss, etc.

  6. #6
    Jr. Mechanic
    Join Date
    Dec 2008
    Gettysburg, Pa.

    Default rough idle

    I agree with k.daddy1, have you had any check engine soon codes, specifically a p0300 ?

  7. #7
    Master Mechanic
    Join Date
    Oct 2008
    Brandon, FLA
    Blog Entries


    Definitely and are there codes as asked? Several issues were relate to this incident and its not the standard tuneup parts. What have your specifically changed recently? At 70mph it smooths out, but when you idle do here a "Vaccuum leak" or a unusual sucking sound?


  8. #8

    Default Same rough idle with my 99 Suburban

    Quote Originally Posted by mrfixdit View Post
    I agree with k.daddy1, have you had any check engine soon codes, specifically a p0300 ?
    Same rough idle with my 99 Suburban and the P0300 code keeps popping up. Plugs, wires, cap, have all been changed.

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