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Thread: Rough Idle Only When Cold. Need Opinion.

  1. #1

    Rough Idle Only When Cold. Need Opinion.

    Hey guys,

    I dont want to start another rough idle thread but I really want to trace this down. Ive searched around and read a bunch of stuff but it seems like it could be a million things if I do it that way and Im tired of spending money on this damn car. Literally everything is shitting the bed on this thing at the moment.

    It started out only slightly and now has progressively gotten worse. Its rough on cold starts. It starts to misfire and the rpms drop for a few seconds, then it recovers itself and the rpm raises, idles fine for a few seconds then drops down a misses again. Once its reaches 200f (operating temp) it runs just fine. No misses at all.

    I started with the easiest thing. I checked all the boots on the coils and reset all the connections. All the boots looked brand new. So I ended up buying 1 new coil to swap through all the coils to find a bad coil and it didn't help. It seems like its something else because it feels like the misses are all over the place, not just one cylinder.

    Throughout all this I never got a code (CEL)

    So I ended up buying a full on BMW scanner since I needed to reset my airbag light.

    Here is what I got

    276D Function check, tank ventilation
    2742 Misfire, cylinder 1
    2745 Misfire, cylinder 6
    2746 Misfire, cylinder 2
    274E Misfire, several cy
    276 Exhaust camshaft sensor: phase position
    2768 Inlet camshaft sensor: phase position
    27C3 Thermal oil level sensor
    2743 Misfire, cylinder 5
    2747 Misfire, cylinder 4

    What do you guys think?

    PS does anyone know what the tank ventilation code would be?

    Thanks for any help.

    05 ZHP 6MT Sedan Titanium Silver

  2. #2
    Join Date
    Nov 2016
    Charlotte, NC
    Jesus. You hit every cylinder there. I'd start by clearing those codes, starting the car cold so it stumbles, then scanning again. Any of those could be stored from some time ago so we can't know what this current issue has set off.

  3. #3
    Thank you. Ill start by doing that. Im wondering if its the 02 sensors. They look original.

    Just realized its probably showing all the cylinders because I was unplugging them while it was running to try and find a bad coil.

    05 ZHP 6MT Sedan Titanium Silver

  4. #4
    Join Date
    Jan 2016
    Chicago area
    I believe if it was the 02 sensors, it would've had an O2 sensor code for that, but don't quote me on that.

  5. #5
    Join Date
    Jan 2013
    Central California
    The O2 sensors are not part of the equation on cold start. At that time the engine is in open loop mode.

    I think you might start trying something completely different. This video helped me to solve my start start issues.

    Seems these M54 engines have poor piston rings that can cause all kinds of issues. I did not do exactly what the video shows. I took a simpler approach. First I did an engine flush with this Then I changed my oil to 6 quarts of Shell Rotella T6 and one quart Mobil 1 0w20.

    Now, my cold engine roars to life when I turn the key, usually hitting 2k. It then idles down and runs smooth.
    Last edited by Dave1027; 03-13-2018 at 12:57 PM.

  6. #6
    Thanks Dave. Oddly enough I was thinking about running some seafoam through it.

    Okay so today I cleared all the codes and this is what I got when I started it up.

    2743 Misfire, cylinder 5
    2744 Misfire, cylinder 3
    2745 Misfire, cylinder 6
    2746 Misfire, cylinder 2
    274E Misfire, several cy

    It sort of feels like the engine is lower in the RPM too fast on a cold engine. It starts bringing the RPMs down really quick. Id say it starts lowering in to under 1000RPM around 70F. Maybe somewhere around 800RPM then it starts stumbling for a few seconds then it will raise it back up.

    Crazy thing is, if the RPMs are ran up with the gas or when it hits operating temp everything is fine. No misses. Even if I let the car sit to where the coolant goes back down to somewhere around, 100F its fine. Only on dead cold starts does it do this.

    Im sure the carbon on mine is crazy. My CCV valve isn't the greatest and Ive just let it go, since its a little expensive and a little bit of a pain to get to. Plus a little oil in the mixture will help keep shit lubed up 2 stoke style, lol.

    Im gonna give the method above a try and see. If I figure this thing out Ill come back and tell you. Im sure there are a lot of other people with something similar. This one is kind of a b to chance down.

    Also Ive been running Mobil 1 0-40W since Ive owned the car, so 30-40k miles.

    Does anyone know if our cars have a fuse that you can pull to cut the fuel? I have a compression gauge, maybe Ill run a check on that too.

    05 ZHP 6MT Sedan Titanium Silver

  7. #7
    Join Date
    Jan 2016
    Chicago area
    My revs drop pretty fast on a cold start too. It doesn't stay at ~1000 RPM for long.

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