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Thread: 99 Grand Marquis “surging” ahead at idle

  1. #1
    Kaysboat Kaysboat's Avatar
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    Default 99 Grand Marquis “surging” ahead at idle

    Hello,

    My Grand Marquis has developed a very annoying issue the past week or so. When it’s in gear, but stopped (at a light, stop sign etc...) it surges ahead a bit. The brakes are more than ample hold the car still, but I can hear and feel the engine surging. But it doesn’t drop off enough to stall out. It doesn’t seem to do it when it’s in neutral, and it’s not an issue at speed.

    I had the issue before and cleaned the mass air flow sensor which seemed to sort it out. I tried that again, and also replaced the air filter, hoping it was an easy/cheep fix. But it’s still the same.

    It seems like a sensor issue, but I’m not 100% sure. I had a look through the shop manual, but all it says for diagnosing the electronic engine controls, is to refer to the Powertrain control/emission diagnosis manual (which I don’t have). In looking at the names of the engine sensors, I’m wondering if it’s the Idle Air Control Valve, to the Mass Air Flow Sensor again.

    Any thoughts?

    Thanks in advance.

  2. #2
    Beater gonna beat sly's Avatar
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    Make sure the MAF is plugged in good and if it is, unplug it and see if there's any change. If not, that's the one with the issue. Pretty much the easiest way to find the problem. If you unplug it and it doesn't change, that's probably the issue.

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  3. #3
    I'm an air-conditioned gypsy gadget73's Avatar
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    Might be worth a snort of cleaner into the idle control motor too. Thats at the other end of the tube coming off the air intake tube.

    Also make sure that air intake tube has no cracks or leaks between the MAF and the throttle body. Splits in the rubber at one of the pleats will cause strange stuff to happen.

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    Kaysboat Kaysboat's Avatar
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    I unplugged the MAF sensor, and it did the same thing but MUCH worse. Wasn’t really comfortable taking the car out of the drive way. So, I’m thinking the MAF sensor is not the issue. Gave it a really good shot of cleaner again just to be sure. I’ll try the cleaner in the idle control motor and have a good look at the tube from the MAF sensor to the throttle body.

  5. #5
    Beater gonna beat sly's Avatar
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    may need to check the ECT function...
    http://www.grandmarq.net/oldfuelinjection/page28.html

    and the air temp sensor (on the side of the air filter box if a 4-wire MAF, pins 1 and 6 on the 6 wire MAF.)
    http://www.grandmarq.net/oldfuelinjection/page29.html

    Other than that, oxygen sensors, TPS, and IAC are pretty much all that's left to go wrong to cause that.

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  6. #6
    Kaysboat Kaysboat's Avatar
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    I took the Idle Air Control Valve apart and gave it a real good shot of MAF sensor cleaner. Also had a look at the tube and other vacuum tubes, and they all looked to be in really good shape.

    This morning it's better, but still doing it a bit. Will try another air valve cleaning and see.

  7. #7
    Kaysboat Kaysboat's Avatar
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    Seems to be running fine this morning. So, I think the issue was the Idle Air Control Valve and a good cleaning did the trick.

    Thanks for the advise and help.

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