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Thread: Can a Vacuum Leak cause the engine to misfire?

  1. #1
    Join Date
    Oct 2003
    Location
    Notre Dame, IN
    Posts
    121

    Default Can a Vacuum Leak cause the engine to misfire?

    I know I just posted a question not long ago but that was for my Mystique.
    Anyways, this question is about my 1999 cougar. Same setup as my Mystique. Is it possible for a vacuum leak to cause the engine to misfire while driving it. The car has a very bad idle, where I have to give it some gas to keep it from dying. Once I do this, the car smooths out while in Park. Then I try to drive it and the idle is terrible. As I was driving I felt the car surge forward and that is when I got a misfire blinking CEL. I am taking the car to a shop but I want to be sure that a vacuum leak could cause the misfire, because I don't want them to read the codes from the car and automatically think that it is the plugs and wires.

    Thanks and sorry in advance if this has been covered before.
    SOLD 5/1/2009:
    '98 Black Mystique LS Duratec V6 2.5L (ATX - Blown 5/25/2008)
    PRT Optimized TB, BAT MAF Adapter+K&N RU-3530, Autolite Double Platinum plugs, rebuilt Sonnax valved VB.
    Mobil 1 - 5W-30, Mobil 1 ATF

  2. #2

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    Quote Originally Posted by Ra\/en View Post
    ....but I want to be sure that a vacuum leak could cause the misfire, because I don't want them to read the codes from the car and automatically think that it is the plugs and wires.
    ....
    The answer is yes. Especially if it is in the intake manifold (after the MAF sensor) or EGR area. I know.

    I had a P0174 and P303 recently. I need to change my EGR gasket (when it gets to 40 and rising) maybe next month .

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