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RPM Fluctuation

Discussion in 'E85 Z4 (2002-2008)' started by mmfiel, Jul 29, 2009.

    mmfiel guest

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    Hi to all!

    Anyone have an idea what is causing an intermittent RPM "surge" (at about 1200 rpm, the motor, without acceleration will run up about 4 or 5 hundred RPM then roll back down). VANOS leak maybe? or maybe 02 sensor? would appreciate any suggestions..thanks
    • Member


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    Automatic or manual?
    I don't see how the engine speed could rise and not cause acceleration while in gear...

    mmfiel guest

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    RPM Flucuation

    It's an Automatic...what I meant about without acceleration is that while "coasting" (no gas pedal pressure) for example at low speed, heavy traffic..the RPM's will surge up and down. It is very intermittent and only at RPM's under 1500. The last mile to my house is a narrow two lane (25MPH) and while I am just coasting, no accelerator pressure, there it happens. Again, not every time and it happened last night going home. The actual flucuation is probably closer to 200 RPM.

    dyerkes guest

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    RPM fluctuations

    You might want to check the Throttle Position Sensor (TPS) and/or your Mass Airflow Sensor (MAF). For the TPS you'll have be savy with electronics troubleshooting. The MAF is simple to access and clean with the special cleaner for the MAF. If you search and don't find anything on this website, try checking on E46fanatics or ZPOST websites.


    mmfiel guest

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    RPM Flucuation


    Thanks, it's driving me nuts since it is so sporadic....hasn't done it now in about 5 days. The MAF I can do, the other....? probably will have to take it to the shop.


    daranco guest

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    similar problem

    Not sure if this is like your problem.... but years ago I
    had a firebird.... and it would intermittantly go into
    "rev spasms" where the engine and tranny would
    go in and out of low gear... sometimes 10-20 times
    in a couple of seconds... giving a real jerky ride.

    After going back to the dealership 13 times (!!! this
    was before the lemon laws)... they FINALLY found
    the problem.... hold on to your hat, cause you
    won't believe it: There was an elec. short in the
    rear-brake-light control switch!!! WHAT????

    Well... it goes like this: When you press the brake
    pedal, there is a switch that turns on your rear brake
    lights. However, that switch has a second function -
    to drop the transmission out of gear (this is done to
    minimize wear on your brake pads... makes sense once
    somebdy explains it).So, since there was a short
    in the switch... every time I hit a little bump, the short
    would send a false signal and the tranny would drop
    out, and then drop right back in!!

    Anyway, your problem might not be like this.... but I
    couldn't help telling this story.

    Good luck

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