Car Problem Reports

Mercury Grand Marquis Problem With Idle Air Bypass Valve May Cause Engine Performance Problems

Mercury Grand Marquis Problem
8 Reports
Me Too

Model Years Affected: 1990, 1991, 1999

Average Mileage: 125,033 mi (75,000 mi - 151,100 mi)


If you experience difficulty starting the engine when cold, stalling at idle, or hesitations during acceleration, it may be the idle air bypass valve. This valve helps the vehicle idle steady when the accelerator pedal is not pressed.

  •  Rookie

    it starts up and than it shuts off but starts back up. can anyone help me with this problem.

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  •  Rookie

    When accelerating between 1st and 2nd gear, there is a lengthy shift time, also I notice when pressing slightly harder on gas pedal while already in travel, it is not responsive as a v-8 should be with quick acceleration. It seems as either gas is not traveling through the gas pump at the required rate, or after getting my intake replaced, that possibly one of the (pistons/cylinders) could be bad, or may have a compression leak. No smoke or stalls and no problems starting when cold. Thanks!

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  • Visitor, , 151,100 mi

    Cold starts difficult (long crank and had to throttle engine to keep idle going.)

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