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5.7 rough idle at start

Discussion in 'General Chevy & GM Tech Questions' started by dancohrs, Apr 12, 2010.

  1. dancohrs

    dancohrs New Member

    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. Silverado Junkie

    Silverado Junkie Rockstar 4 Years 500 Posts

    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: Apr 12, 2010
  3. dannys99

    dannys99 Rockstar

    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.
  4. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    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...
  5. cobra2end

    cobra2end Rockstar 100 Posts

    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. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    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

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