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Fluctuating RPMs on idle and loss of power throughout RPM range

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    Fluctuating RPMs on idle and loss of power throughout RPM range

    Hey r3v,

    Friend has been having a bit of trouble with his car over the past months and can't seem to find the source, thought I'd ask around here for him.

    He owns a '91 325i 5mt vert. About 8 months ago, his car started fluctuating between about 1800 to 300 on idle until it just stalled and died out. Since then, he has replaced his spark plugs, coolant temp sensor, o2 sensor, and mass airflow. He replaced his distributor cap and also checked his idle control and it seemed to be fine. Compression test showed things were within spec.

    After doing these thing's his car ran fine for about 2 weeks before starting to throw an a/f error. Whenever his car was in idle for more than 5 seconds, the red CEL would come on but when you tapped the gas to rev, even the slightest bit, it would disappear.
    Also, when left in idle for a while, his car would start fluctuating revs again, though different from the first time. This time the car had to have been sitting in idle for sometime (at least a minute whereas the first time it was immediately on idle) before it started surging and when it did, it wasn't as drastic as the first time. Roughly 1300 to 300 til eventually a stall.

    Sprayed around the engine bay a bit with carb cleaner and found a vac leak. He got that fixed and when he started the car, it was idling at about 2300. Accelerating, the car felt robbed of power and struggling. When left to idle for a bit, it started it's fluctuations again.
    On a whim, while his car was in idle, he went and unplugged the MAF sensor and the car's idle went down to normal and stayed steady. He didn't try driving with it out though, just put it back in afterwards.

    Does anyone know what could be causing this?
    Web Designer / Front End Developer
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    #2
    There are intake leaks. A smoke test will find them.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment


      #3
      Take apart the intake manifold and throttle and replace the gaskets. Swap the afm back to a known working one.
      The check engine light on idle is very common and is a hint of a vac leak. M20s are retardedly sensitive to vac leaks. Also check the booster check valve.

      Comment


        #4
        Most likely an air leak. You may also have corrosion in the round electrical connector under your intake.
        90 325i DD/Track
        03 Durango 5.9


        Originally posted by e30mpg
        It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

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