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Thread: Random misfire at idle, PLEASE HELP!!

  1. #1
    Join Date
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    Random misfire at idle, PLEASE HELP!!

    so my car started acting up about a month ago. I'm having a misfiring issue. It only does it at idle or at lower rpms. Most of the time it happens when i'm at a red light. When I'm sitting there, it will be idling fine, then all of a sudden the rpms will drop and it will run really rough. almost sounds like its a boxer engine or something..Sometimes it goes away when i give a quick blip of the throttle but most of the time i will have to shut it off, wait a few seconds and re start it. then it will run fine.. heres what I've tried so far.. fuel filter, new plugs, cleaned icv and mass air sensor. did seafoam. cleaned throttle body. I am getting really annoyed, maybe you guys have some ideas? any help would be appreciated

  2. #2
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    I personally wouldn't trust just cleaning the ICV, but that is just me.

    There is also the throttle position sensor to consider.

    A vacuum leak is another one.

    If it's really a misfire then check your coil packs since you already replaced the plugs.

  3. #3
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    is the check engine light coming on? If so. swap out plug, coil, and fuel injector on that cylinder.

  4. #4
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    My rpms would drop here and there at idle, it would almost make the car stall. i was told to check the idc and this and that, but in the end it ended up being a bad Throttle positioning sensor, that didn't throw a cel until it decided not to work anymore.
    -97 ///M3-R.I.P.. 01 330ci-Sold.. 96 S/C ///M3-Sold.. 03 530i.. 93 Vigor-

  5. #5
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    I had same exact problem recently.. Ended up being the upper chain tensioner

  6. #6
    Join Date
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    Check your coil boots, regap plugs, clean ICV.
    1997 Arctic Silver/Black M3
    CES Stage IV (651rwhp/615rwtq @ 24 psi)

    1999 Techno Violet/Dove M3
    Auto/Convertible and staying stock!

  7. #7
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    thanks guys, those are all really good ideas. I think the next step is to swap coil packs and see if the misfire follows to that cylinder. ill have to see if I can get a code scanner/reset tool...also changing that throttle pos sensor doesn't sound like a bad idea. thanks again for your input guys

  8. #8
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    ok, here are the codes that came up with the code reader....
    p1250-fuel pressure regulator control fault
    p0300- pcm has determined that random misfires have occured
    p0304- misfire cyl 4
    p0305 -misfire cyl 5
    p0306 -misfire cyl 6
    p0155- o2 sensor bank 2 sensor 1
    p0161- o2 sensor bank 2 sensor 2

  9. #9
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    Ok, lets go down the list. Seriously.

    Fuel Pressure, underload and @ idle.
    How old are the plugs?
    Dead packs?
    Vaccumm leak?
    Broken ICV
    Z3 - S50 - OBD2 - Smog Legal - 6 Speed - 3.46 - Anthracite

  10. #10
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    Quote Originally Posted by bigmitch117 View Post
    ok, here are the codes that came up with the code reader....
    p1250-fuel pressure regulator control fault
    p0300- pcm has determined that random misfires have occured
    p0304- misfire cyl 4
    p0305 -misfire cyl 5
    p0306 -misfire cyl 6
    p0155- o2 sensor bank 2 sensor 1
    p0161- o2 sensor bank 2 sensor 2
    ?? limp mode.

  11. #11
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  12. #12
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    Quote Originally Posted by Devius1 View Post
    ?? limp mode.
    Sounds like more a vaccum leak, a bad ground, or a bad MAF
    Z3 - S50 - OBD2 - Smog Legal - 6 Speed - 3.46 - Anthracite

  13. #13
    rcM3 is offline baaaaaaaaaaaaaaaaaaaah...
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    O2 sensors as a start. Replace both pre-cat sensors. They're expensive (~$100), but if you don't do them now (when they need to be done) you'll end you replacing all four and your cats.

    I'd check your coilpacks/boots too, but strictly based upon your codes, it's likely all your problems are coming from your O2 sensors.

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