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Thread: P0300, P0174, specific cylinder misfires - help please!

  1. #1

    P0300, P0174, specific cylinder misfires - help please!

    Hi Mafia, I've read about this issue for several days and can't really figure out where to proceed. I don't do a ton of my own work, so forgive the na´vetÚ.

    The other day, with no prior warning, my car started making these awful vibrations and lawnmower/helicopter-like noises when I hit the gas (no problem when foot was off the gas). I looked up the symptoms, figured it was a misfire, ordered and received an ODB2 scanner, and sure enough:

    P0300
    P0305
    P0306
    P0174

    I understand the 5/6 are specific cylinder misfires, but the P0300 random misfire has me stumped. I figured it was probably my coils, since my plugs were changed about 30k miles ago, and that seems fast for them to wear out. A few days and a bit of driving later, today I swapped coils around, and it SEEMED as though the misfires were following the coils, but I scanned it again, and the P0174 is gone, but now FOUR cylinders are misfiring, and the P0300 is still there.

    However, When I disconnect each coil, I can hear a change in the engine noise, which to me suggests that all the coils and plugs are actually fine (6 might be genuinely bad, hard to tell). At idle, or in gear with the clutch pedal depressed, there is a very noticeable, rhythmic knocking/tapping noise that gets louder the more coils are disconnected. When I get back in the car, all coils connected, and hit the gas while in neutral, the noise stops, though the car still feels like it's misfiring, with loud general engine noise and vibrations.

    Does this sound like bad coils or plugs? Does the phantom P0174 suggest a vacuum leak somewhere? I bought the car 30k miles ago knowing it had a slightly cracked lower intake boot, which I never did anything about, but it seemed to be fine for 3 years. Could it be the DISA? MAF? Could it be a compression issue in the cylinders? What would cause more and more cylinders to misfire?

  2. #2
    Join Date
    Jun 2011
    Location
    VA/DC
    Posts
    14,440
    The 0174 is most likely the boot (and/or other leak) id replace both. Considr doing the disa and cleaning throttle body and idle control valve while you have it apart. Also be sure to have an extra "F" connector on hand. Sorry I can't help on the other codes.


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  3. #3
    Misfire Cylinder 4

    Good evening Mafiosos! I hope you are all well. Quick question since this is the first time this has ever happened to my car. So, while driving home from work yesterday the service engine light came on. As soon as it did, the engine began running rough for about 20 minutes of the commute then turned off. Once off the car ran smoothly all the way home (another 30 minutes). Parked and let it cool down before taking a look. I used my scanner and the only message I'm getting is: Misfire Cylinder 4.

    My car is a 2005 330Ci with ~83k miles on the clock. I get it services regularly but never had to replace the sparkplug or coils.

    What should do to further diagnose the problem or isbit as straightforward as a bad plug/coil. Wondering if this is something I can tackle myself and possibly save a bit of $.

    Any feedback/guidance will be greatly appreciated. Thank you in advance and have a great weekend!!


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  4. #4
    Autozone.com
    Sent from my SM-N981U using Tapatalk

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