M54 3.0i erratic idle, stalling - MAF?

[pokeybritches]

I've had my supercharger installed for about 2000 miles (writeup to follow... eventually). After getting everything sorted out with the install, the car had been running flawlessly. I've taken it on spirited drives without a hiccup. I'm very happy with the finished product, and I don't think my current issue is related.

I parked the car for several weeks while I went out to the west coast for job interviews. When I came back and fired it up, it idled very erratically with an EML, yellow brake light, SES, and yellow triangle lit up (more on this "mode" in a bit). I stopped and restarted the car, and the lights disappeared but the erratic idle remained. Rpm did the following: bounced between 600-1200 rpm for several seconds; maintained a steady state rough idle at around 800 rpm for several seconds; climbed steadily to over 2000 rpm before falling back into 600-1200 rpm oscillations.

I've had to drive the car to and from work (I only live a couple miles away) for the past two days. I've driven it like an 80 year old grandparent, and any more than the slightest throttle application sends the car into that "mode" I mentioned earlier - EML, SES light, triangle, yellow brake light... and unresponsive to any throttle input at that point. The only thing to do is restart it. When I clutch in, the car dies half the time. However, as the rpm climbs over 2000, everything smooths out like nothing is wrong.

On day two I got codes with both O2 banks rich.

1. I've checked, double checked, and triple checked all my hoses and piping from the supercharger. To have enough unmetered air coming in to get the car to act this way, I would have to have a very serious vacuum leak.

2. I unplugged the MAF sensor and everything smoothed out. Once the O2 sensors warmed up, it drove buttery smooth. I haven't given it more than 1/4 throttle input.

3. I disconnected the battery for 30 minutes to reset the ECU.

4. I cleaned the MAF sensor, plugged it back up, and the erratic idle returned immediately upon startup.

Before I throw down $350-400 on a new MAF sensor, is there anything else I should check? Has anyone had a MAF sensor suddenly stop working? Most dirty MAF sensors slowly cause problems; I haven't read any threads about the sensor failing totally and unexpectedly. I know oiled K&N filters can affect MAF sensors, but the car had been working well prior to sitting for a few weeks. I don't think I over-oiled it, and it couldn't have dripped onto the MAF sensor based on the filter's location.

I swear my car is a woman. It treats me well when it has competition (the M)... after I commit and it has me all to itself (stored the M), it goes psychotic and all these hidden problems manifest themselves, like a $275 HID headlight failing literally the moment I returned home. It wants money, and more money, like the new shoes (wheel/tire) package I bought it 2000 miles ago are a distant memory . I paid tons of money for cosmetic enhancements, and now it wants more retail appeasement .

[mpm3]

a lot of times ( and i can be totally off ) mice and such get in when a car sits and eat threw the wiring harnesses. just a random guess i could be totally wrong just trying to help a brotha out

[zgood4u]

I have the same issue with my M coupe currently. It is the most maddeningly tempermental problem. It would be fine and start with no problems then out of nowhere the car would sound and feel like it's choked up. I would have to re-start it anywwhere from 5-8 time before it would clear and then the SES light would stay on and then disappear after a few other re-starts. It's at the dealer now and they're replacing the MAF sensor.

[pokeybritches]

Were you able to pull the codes?

I highly doubt animals got into the wiring. The car only sat for two weeks, and I don't live in an area where they are a problem. When I extended the wiring harness for the MAF sensor, I encapsulated it in plastic tubing.

[zgood4u]

I don't have the codes but my SA at the dealer left for the day on Friday late. I'll have the info tomorrow.

[pokeybritches]

On driving with the MAF sensor unplugged:

1. Upon cold start, the car immediately goes into that mode with EML, triangle, yellow brake, SES, rapidly oscillating idle, etc. lit up. I tried stopping and restarting the car 10 times before unplugging the battery cable for 30 seconds as a last resort. The car then started up fine, with an SES light due to the MAF sensor being unplugged.

2. Before you drive anywhere, let the car warm up. If you don't, the car will stall. I believe this is because the car relies heavily on the O2 sensor readings for fuel maps, especially when the car is in speed density mode (MAF sensor inoperative). O2 sensors don't give accurate readings until they reach a certain temp. I've found that when the coolant gauge reaches normal operating range, the car is good to go.

3. If you have to drive the car, drive it like a grandma. AFR's will be all over the place. Driving without a MAF sensor will get you home, and that's about all it's meant to do.

4. Tomorrow, I'm going to experiment with turning the key to the ON position without starting the car to try and give the O2 sensor heaters time to warm up the O2 sensors.

If it wasn't for the daily torrential downpours the gulf coast experiences this time of the year, I'd walk the few miles to work. The car runs very smoothly once it's warmed up, so I don't think it will do any damage to drive it for a very limited time. I deploy in less than a week, so I'll leave this project for when I return.

[pokeybritches]

Update: Swapped MAF sensors with a friend's E46 330ci, and the problem went away.