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  1. #1

    Default 5.7 rough idle at start

    I have 1998 Chevy 4x4 w/5.7
    in just the last week my fuel mileage has become terrible and when I start truck engine idles rough and smokes out exhaust then smoothes out.
    Seems to run fine during driving but after you shut it off and restart it barely idles and blows white
    smoke,runs very rough and then smoothes out again.
    Also seems to be faint smell of gas. Ihave checked for leaks and have found none.

  2. #2
    Master Mechanic Silverado Junkie's Avatar
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    The only thing i know that causes white smoke is when your burning coolant. Coolant from a leak somewhere on the motor is slowly seeping in your combustion chambers as your truck sits, then when you fire it up, the coolant dosnt burn well so it causes you a rough idle. Then when the coolant in your cylinders is burnt up, you truck goes back to runnin good. You dont notice it while driving because the leak is so slow.
    Last edited by Silverado Junkie; 04-12-2010 at 09:06 PM.
    1995 Silverado,Z71, 3-inch lift,2-inch leveling kit, SkyJacker Suspension, short ram-air intake, throttle body spacer, MSD ignition coil, straight pipes

  3. #3
    Sr. Apprentice dannys99's Avatar
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    My 99 did the same thing sometimes, I had a coolant leak in the intake manifold gasket, you couldn't see water in the oil but it cause the engine to steam inside and put moisture in the distributor cap. I bet if you change the cap and rotor it will run great for a month or two and then do the same thing.
    "If I were lie'n I'd be cry'n and I aint shed a tear"

  4. #4
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    Check your Fuel pressure regulator (located on the back of the spider injector under the upper intake).. It might be bleeding off into the intake. Causing the white smoke since Raw fuel can have a similar effect... Clean your IAC wouldnt hurt either. Change your fuel filter...
    Mike

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  5. #5
    Jr. Mechanic
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    Sounds like the intake gasket.I just replaced mine on my 97 5,7. is not to bad of a job to do. lots of wires to move out of the way.

  6. #6
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    the vortec 350(5.7) are pretty notorious for the intake gaskets to go, but word of advice is just do all the gaskets at the same time, head, intakes and valve cover. you already have it half way ripped apart anyway
    99 K1500 Suburban LT "THE BEAST"
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