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Thread: rough idle... again...

  1. #1
    Join Date
    Nov 2004
    Posts
    205

    Default rough idle... again...

    here we go again...

    my car is idling rough again...

    here is the problem this time...


    when i turn on the car.... the idle swings from 1500 - 1800...
    when i turn on the aircon... idle stabilizes at 1200...
    when i engage the gear... its at 800...

    d problem is when the car reaches operating temperature...
    regardless of whether the aircon is on or off... idle swings from 1200 - 1500

    when gear is engaged... no rough idle...

    help pls...

    thanks!

  2. #2
    Join Date
    Oct 2006
    Location
    Reading, UK
    Posts
    1,853

    Default

    Quote Originally Posted by pong
    when i turn on the car.... the idle swings from 1500 - 1800...
    Massive Idle swing is almost always due to a huge bypass of the MAF/Air flow unit.

    Have you checked for a massive vaccuum leak yet?

  3. #3
    Join Date
    Jun 2006
    Posts
    76

    Default

    Could you evaluate a bit Ferret?

    Think of me as the ultimate NEWB.

    My 94 540 seems to be doing the same thing, but not to the extent that "pong's" is. How do I... Check for a hole in the hoses? which one's?
    Last edited by rcbrown23; 08-19-2007 at 01:15 PM.

  4. #4
    Join Date
    Oct 2006
    Location
    Reading, UK
    Posts
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    Quote Originally Posted by rcbrown23
    Could you evaluate
    Elaborate?

    Quote Originally Posted by rcbrown23
    a bit Ferret?

    Think of me as the ultimate NEWB.

    My 94 540 seems to be doing the same thing, but not to the extent that "pong's" is. How do I... Check for a hole in the hoses? which one's?
    Okay, I'll stop being a prick now.

    If it's doing it on a 540i you're going to want to set the car on fire shortly I think... you'll be looking at manifold gaskets or pcv gaskets, both of which are a bitch to do...

    Stick your head under the bonnet and see if you can hear the car making a hissing noise while it's doing it, that's usually the first sign.

  5. #5
    Join Date
    Jun 2006
    Posts
    76

    Default

    Ouch. And... Ouch.

    Tomato, Potato... I'm hungover
    Last edited by rcbrown23; 08-19-2007 at 02:07 PM.

  6. #6
    Join Date
    Nov 2004
    Posts
    205

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    crap... all the hoses... and i couldnt find it...
    is there an easy way? tried spraying water on the hoses... so that if engine acts weird... then i have found d air intake leak...

  7. #7
    Join Date
    Mar 2006
    Location
    Maryland, Virginia, D.C.
    Posts
    705

    Default

    I agree with Ferret. Manifold gasket/vacuum leak. Secondarily, the idle control valve.

  8. #8
    Join Date
    Nov 2004
    Posts
    205

    Default

    ok... im about to dunk this car into the lake...

    it recently got a top overhaul... vacuum leak...
    which in particulr....

    did the water thing to all the lines going to the throttle body... none reacted...

    idle control valve... placed a working one in there... no change...

    maf too....

    seals in oil cover, dipstick are ok...

    what else should i look at?

  9. #9
    Join Date
    Jun 2007
    Location
    Cheshire CT
    Posts
    310

    Default

    I know it's a different engine, but on my 535 it wouldn't idle at all when the coolant temp switch went bad.

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