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      12-08-2012, 03:54 PM   #1
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Drives: 2009 E92 335i 6MT
Join Date: Sep 2012
Location: Sterling, VA

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"mixture control" code and wet #6 plug

Hi all,

today I decided to do a little maintenance on my car - 2009 E92 335i, 6MT, about 72K miles. I had no record of the plugs having been changed so I figured it was overdue. The only issue that I'd been having with the car was occasionally - not all the time, just maybe 50% of the time - at say about half throttle or there abouts, I would get what I could call "choppy" acceleration, like I was bouncing my foot on the gas pedal or something instead of holding it steady. Well, I got all the old plugs out without issue and they all looked pretty much like normal used plugs, except for #6, which came out wet and smelling of gasoline. I don't think there was any oil involved as after only a minute or so out of the car it was dry however it was still black. I checked my codes (I have no CEL) and the only code that came up was "Mixture Control" I neglected to write down the exact code (dumb, I know) but I think it was P29E0.

I drove the car last night, but this morning only started it up to pull it in the driveway before I started changing the spark plugs.

If the issue persists I will definitely recheck that plug. If it is wet again, what do you think the likely culprit would be? I would guess either coil or leaky injector on #6, does that sound reasonable? If it were the coil, would I not be getting a misfire code however?

thanks for any insight from anyone who's had a similar issue and successfully resolved it.

Edit: I forgot to mention, when I restarted the car after putting everything back together, it took longer than usual to catch and ran a little rough for a minute or so but after revving it a couple times it seemed to "clear its throat" and seems to be running OK now. I have not had any noticeable hard start/ rough running issues up to this point however. Not sure if this is related or not or if that is normal for a plug replacement (although the only things that were disconnected to get access to the plugs were the one sensor on the cabin air filter tray and the hood switch for the alarm system, so I'm not sure how that could have messed anything up?)

Last edited by N8N; 12-08-2012 at 04:02 PM.