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1991 Mercury Grand Marquis - engine stalling

1991 Mercury Grand Marquis, 5L V8, about 65,000 original miles: Has run perfectly for a long time; recently, engine began stalling when coming to a stop or sitting at lights, idle is very low now, sounds a little rough when doing quick-rev on engine when parked.

Anybody know what to check, other than call a mechanic right away?


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First thing that comes to mind is a clogged catalytic converter. Have someone rev while you put your hand next to the end of the tailpipe. Look inside for obstruction. It should be harder to not have your hand move as the engine races and it should sound clear and not muffled. Has this been coming on over a period of time or has it been sudden? Does it run OK for the first few seconds after starting for the day and then starts to die?

Posted on May 08, 2009

  • yadayada
    yadayada Nov 01, 2011

    The catalytic converters do not plug on this year, this is wrong.


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The most common fault on this engine based on my 20 years at a Ford dealer is a sludged up throttle valve butterfly and a sticking idle speed control air bypass valve, very common problem and numerous service letters issued to fix the problem.
Use the following procedure to clean the sludge out of the these parts and restore idle quality.

To correct this problem get a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, spray it into the air intake of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speeds problems you may need to seek the help of a professional.

Posted on Sep 30, 2011


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