[Thomachaan]

I believe I have a failed MAF based on codes, performance, and symptoms. I have a new MAF and DPS coming in to confirm, but thought I'd share what I think caused it to fail and hopefully learn something from y'all.

My car (09 328i xDrive N51) was down for ~3 months over the Winter. I worked on various systems to diagnose and get it running again. One cloned DME and gear position sensor later, it's running!, but running rich with a not-so-good idle. I see soot on the exhaust tips as well =[

Codes:
P0172 (29E0) - System too rich bank 1
P0175 (29E1) - System too rich bank 2
P1105 (2D29) - DME: Differential-pressure sensor, intake manifold: plausibility
P00BD (2D06) - Mass or Volume Air Flow 'A' Circuit Range/Performance - Air Flow Too High

My Theory:
Leaving the airbox w/MAF out in my garage for long periods of time may have caused dust to settle on the hotwire, which in turn causes MAF to use more current to maintain wire temp, causing car to assume more air flowing in than there actually is, also causing implausibility code from DPS. I've used MAF cleaner to no avail, crap must have cooked in by now. For sure my MAF was introduced to elements it never would have seen had it stayed in the car.

Also, while thoroughly cleaning my intake, I removed and cleaned the DPS, with CRC MAF cleaner and maybe 97% isopropyl alcohol at one point. No clue if it's working as it should.

Rather than spending another few months to figure out exactly how to diagnose each sensor, I opted to throw parts this time. These sensors appear to be non-serviceable internally, but if I can figure out how either failed, hopefully I can avoid having to buy these again ever.

I don't want to be fearful of cleaning these sensors, but the info out there on the webs isn't accurate enough about our specific engines and what exactly causes them to fail. There's gotta be surefire methods to clean these.

[3PedalJake]

It's also possible the MAF is accurate and you actually do have air flow too high due to air leakage into intake. Unplug the MAF connector, if the idle improves it is probably an intake leak and not the MAF sensor.

[Thomachaan]

Update: I replaced both the MAF and DPS, bought from FCP Euro. Car runs close to brand new.

I also removed the 3 stage intake manifold to check for a clog, like a rag or paper towel. All clear inside. Months ago I cleaned the PCV angled heater and fixed the big DISA valve with epoxy and a new shaft seal (autozone fuel injector set had the right size), still looking good.

After feeling the issues go away and remembering how it drove before the car went down months ago, I believe my MAF was on its way out for a while. Slow degradation makes sense for such a delicate sensor design. That hot wire in the MAF should be fricken replaceable!!

My gear shifts have improved, sluggishness greatly reduced, no more black soot shooting out my exhaust, and the throttle response from a full stop is better than I've ever known it to be. It's not as responsive as my cable throttle 99 Sienna, but for a powerful engine this is probably better and safer.

Last remaining issues that affect drive response:
->I changed my alternator pulley but still need to get those 2 internal bearings replaced. They're audible.
->Oil pan gasket, could be a *very* slight vacuum leak.
->Drain/fill transmission one more time, Valvoline Multi-Vehicle Dex VI ATF.
->Drain/fill rear and front differentials.
->Drain/fill transfer case, then clear VTG code in ISTA.
->Clean fuel injectors, replace seals.
->Replace all O2 sensors, peace of mind that the DME is seeing everything as clear as possible.

Originally Posted by 3PedalJake

It's also possible the MAF is accurate and you actually do have air flow too high due to air leakage into intake. Unplug the MAF connector, if the idle improves it is probably an intake leak and not the MAF sensor.

The car was running rich and I used a smoke leak detector on the intake, no leaks at all. I'd think a leak would run the engine lean.

[marvinstockman]

Next time, you can just try cleaning the MAF with MAF cleaner.

[3PedalJake]

Originally Posted by Thomachaan

Update: I replaced both the MAF and DPS, bought from FCP Euro. Car runs close to brand new.

I also removed the 3 stage intake manifold to check for a clog, like a rag or paper towel. All clear inside. Months ago I cleaned the PCV angled heater and fixed the big DISA valve with epoxy and a new shaft seal (autozone fuel injector set had the right size), still looking good.

After feeling the issues go away and remembering how it drove before the car went down months ago, I believe my MAF was on its way out for a while. Slow degradation makes sense for such a delicate sensor design. That hot wire in the MAF should be fricken replaceable!!

My gear shifts have improved, sluggishness greatly reduced, no more black soot shooting out my exhaust, and the throttle response from a full stop is better than I've ever known it to be. It's not as responsive as my cable throttle 99 Sienna, but for a powerful engine this is probably better and safer.

Last remaining issues that affect drive response:
->I changed my alternator pulley but still need to get those 2 internal bearings replaced. They're audible.
->Oil pan gasket, could be a *very* slight vacuum leak.
->Drain/fill transmission one more time, Valvoline Multi-Vehicle Dex VI ATF.
->Drain/fill rear and front differentials.
->Drain/fill transfer case, then clear VTG code in ISTA.
->Clean fuel injectors, replace seals.
->Replace all O2 sensors, peace of mind that the DME is seeing everything as clear as possible.


The car was running rich and I used a smoke leak detector on the intake, no leaks at all. I'd think a leak would run the engine lean.

You didn't mention that in your original post, glad you got it sorted. If there's a leak, and it doesn't have to be big the DME will be confused about fueling, that's the rough idle and yeah it can throw rich codes. I had all those codes and symptoms as well, along with some misfires, they are what should happen when the MAP isn't what it should be according to airflow reading from the MAF, that's the implausibility. Mine turned out to be a loose CCV hose, and the ancient looking MAF sensor with the broken connector tab still works fine. Not saying yours didn't go bad, I mean they do go bad sometimes but I don't think they're as fragile as you're suggesting either. For sh!ts and giggles try plugging the old sensor back in now that you've put everything back together again.