95 M3 intermittent power loss, CEL off and on

[jmejia15]

Yesterday, M3 started to feel like it was losing some power, not pulling as hard as it normally does. (mods: 3.5" intake with 540 HFM bimmerworld boot, 21.5 injectors, TRM chip, magnaflow cats, ACS catback)

When I reach 5k RPMs, the check engine light turns on and as soon as I left off the gas or switch gears it goes away. I did the pedal trick and got the code 1215, which reads Air flow sensor fault, leading me to think its either a faulty HFM or a vacuum leak somewhere.

How would I be able to pinpoint the problem? Unfortunately, I do not have another HFM to swap and find out

UPDATE: I replaced the HFM, and the problem had gone away. However the problem has returned now and the code reads 1222 and I am pretty sure it is not the O2 sensor since that wad replaced not even a year ago. Any ideas? Maybe it is an actual vacuum leak, any leads would be appreciated.

Also, I'm running Bosch 21lb injectors, the PO said they were better than the 21.5lb equivalents and that they ran fine with the tune. Is this true, could it be the cause for the issue that I'm having?

thanks

[jmejia15]

Bump, anyone experience this before?

[TAMUmpower]

Spray the element of the HFM with HFM cleaner or soak the whole thing in rubbing alcohol first.

Probable cause #2, oxygen sensor

Probable cause #3 knock sensor

The ECU is kinda known for displaying false error codes for other things when an oxygen sensor is out. My knock sensor code came up and stayed on even after I replaced both knock sensors...turned out to be oxygen sensor.

[jmejia15]

update: I cleaned out the HFM and put it back on, now it is a fixed CEL, stays on all the time, even at idle. same code too, 1215. Is that a definite faulty HFM because after I cleaned it out, the CEL stays on all the time?

Thanks

[sjpgoalie]

update: I cleaned out the HFM and put it back on, now it is a fixed CEL, stays on all the time, even at idle. same code too, 1215. Is that a definite faulty HFM because after I cleaned it out, the CEL stays on all the time?

Thanks

How did you clean it?? They're extremely easy to ruin..

[jmejia15]

MAF cleaner of course. I think I am going to have to do a smoke test to pinpoint if there is a vacuum leak.

[sjpgoalie]

True that. Might as well before you go buying another. Makes me think it deff is the hfm now that the light is solid after cleaning it..

[CMG]

U should never have to clean a maf unless it's obviously coated in oil.

[jmejia15]

Bump. first post updated

I forgot to mention that this morning idle was pretty rough, falling below 500RPMs and actually stalling out twice before I even moved the car

[jmejia15]

Ttt, what would be next to rule out?

[KaptinKP]

Knock sensors? I also got the maf code but it turned out to be my knock sensors. =/

[CMG]

Knock sensos would explain the intermittent cel but not running rough. Did u check for vac leaks?