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Old 03-10-2006, 12:10 AM
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M3 stumbles/dies/runs bad - code 1215 mass air flow - please help!!

Symptoms:

It has always had a shaky idle. The kind that goes smooth for 15 seconds then rough for 15 seconds, back and forth. It has been in the 30s-60's outside up until this week.

At some point when I was trying to figure out what is causing the shaky idle, I disconnected the mass airflow sensor to see if it ran better. I read that if you disconnect it when the car is off, then run the car to see if it works better, then reconnect the mass airflow sensor when the car is once again off, that it would not screw anything up (but it might set a hard code or something). Well I followed that procedure. I don't know if it's related to what's happening now...

Three days ago, I started the car up cold in the morning, ambient temp maybe 50-60 degrees, and it ran very very rough, stumbled a bit, but I revved it a little and it seemed to straighten itself out. The car sat for 3 days while I was out of town, and tonight I went to start it up, it ran horribly and practically stumbled itself to death. I turned the key off before it could die on its own. I tried again about 15 seconds later, same result. Car made a gasoline/exhaust smell a bit, as well (it usually does a little bit, but it was more prominent now, maybe its just my imagination.) Then I waited about a minute and re-started it, it ran less roughly but the engine made a distinct slapping "clack clack clack clack" sound, RPM-dependent. Anyway... I do the 5-tap trick to run the codes on my car - i get a 1215, which is apparently the air mass/mass volume sensor. The thing is, would this really be occurring because I (perhaps "properly" as you could say) disconnected the MAF sensor over a week ago? There are many times this car has started/run fine inbetween the two times that this stumble/die behaviour has occurred. I'd think it would happen every time I started it, but maybe that's the enigma of the M3...

Also, if I set the 1215 code "hard" into my car, would removing the code cause this problem to go away? Would a peake reset/code tool do the trick? I can't find info anywhere about this.

a new AFM is $300... I do not want to replace this part "on a whim"...

Last edited by TheNorthWaves; 03-10-2006 at 01:23 AM.
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Old 02-11-2007, 02:08 PM
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Sounds like your MAF is reading faulty and causing variation inside your engine timing which is initiating detonation. From what you've described, this could be very likely. Pull your spark plugs after it has run. They should be "coffee with cream" brown and dry. If they are anything else, I would try borrowing an MAF from a friend and see what happens. Also, you can purchase MAF cleaner. They sell it at most major autoparts stores. This could clear it up.. One possible other cause could be that your top end is leaking off oil. The heads have check valves that are designed to retain oil in he head and release it upon startup. If yours isn't doing that, it would cause the lifters to create an rpm dependent clacking sound. Check your oil level and run an additive. See if this straightens it out. A misfire can have many causes, so check carefully.
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Old 02-13-2007, 03:51 PM
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do you have a aftremarket cai. If the filters aren't kept clean and dried properly they can kill a MAF . just another thing that could cause it.
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Old 02-19-2007, 11:13 AM
 
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i would start with clearing all codes and thoroughly (and carefully) cleaning the MAF with a specific MAF cleaner. i would inspect the air filter and i would also carefully inspect all of the MAF wiring.

then.. start the car dead cold and see what happens.

the clack clack noise concerns me.. and that is likely not related except by way of the RPM dropping way too low.
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Old 02-25-2007, 09:51 AM
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You might have a vacuum leak. Mine did the same thing recently. It would throw all sorts of codes at me, I believe one of them was MAF too, mine is ODB2 though so I got other stuff that you wouldn't get.

Vacuum leaks confuse the hell out of the computer, mine ended up being the crank case gasket. But it could be anything. Check all your hoses to make sure you don't have any holes anywhere.
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Old 02-25-2007, 02:30 PM
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My car was running pretty rough for a while and I checked the codes and it came up with the Mass Air Flow code, I replaced the mass air flow and it fixed the problem. I would start there. Usually when those go bad the engine is pretty lumpy because the fuel to air ratio gets screwed up.
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Old 02-26-2007, 04:33 PM
 
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before you drop hundreds on an MAF.. clean yours.
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