Question about 1999 Chevrolet Silverado 2500

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99 chevy silverado Unstable idle when it worms up

Hello i have a 99 silverado 6.0 that when it warms up the idle is unstable it goes up and down or when i come to a stop. once i go park or neutral the idles is fine, its just when it goes into drive or reverse its starts to act up. I have cleaned the throttle body replace the idle air control checked the fuel pressure and it is fine. is there someone that can help thanks.

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  • flores_63 Feb 07, 2009

    hey i have also replaced the mas and it did not help. i also have checked for vacum leak have not found any.

  • MotoXFreak19 Apr 14, 2009

    this is going to sound weird but mine did that... (99 silv. 2500 4x4 6.0l) and when i put it in gear it would bog way down (once it stalled) but i put new plugs and wires and it cured it...



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It sounds as if you have a small vacuum leak some where in the intake system. Also since you cleaned the throttle body also clean the MAS. It is located between the air filter housing and the throttle body. Hope this helps, rate me highly.
RPM Northwest

Posted on Feb 07, 2009

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Check the engine mountain rubbers ,, one or more of them is broken and needs to be replaced.

pop the hood, start the vehicle and move it from park to drive to reverse with the brake pedal down and you will see the engine moving. the broken mounting rubbers are the cause for this.

Posted on Feb 07, 2009


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