M50TU..mass airflow sensor issue??

[will308]

Hello everyone.
I have a strange problem that just started today. I did a search and couldn't find anyone with the same issue.
The car is a '95 525i, I bought it a few years ago with 170,000 miles on it and just yesterday it turned 212,800..most of them uneventful.
Car has been running very well until today, when I see the check engine light flicker and then go out. No issues with drivability until I come to a stop sign.
Just as I stopped, the engine surged and then just died.
Fired right back up and ran fine(on the freeway at 80 mph)except for the occasional check engine light.
Got it back to the house and ran a Peake code search and came up with code 29..mass airflow sensor?? I cleaned it (MAF) and ran the car for a bit and it seemed OK, but came to a stop sign and although it didn't die...it surged again, like the transmission tourque converter didn't decouple but it settled down quickly and then drove fine. I drove it for a bit and the check engine light will come on but I don't know how to check the mass aiflow sensor to see if it really is the problem.
Hopefully someone can point me in the right direction.
Thanks,

[Hofmeister]

Vacuum leak? Mass airflow and o2 sensor codes are easy to trigger

[will308]

Wow that was quick....lol
Thanks, I looked at the intake boot for signs of cracks and all of the associated lines and didn't see anything obvious???

[will308]

Car started fine this morning. drove 15 or so mile to work without a hitch....everything running smootly...then all of a sudden the check engine light comes on and the car dies at a traffic light. I'm beginning to think it's an electrical or sensor problem. I disconneted the MAF and no change in the idle...when I reconnect it the engine sputters...Bad MAF????
Thanks,

[twastheglow]

I'm certainly no authority on the subject, as my E34 is "new" to me too; but I will say on the E39M, disconnecting the MAFS and running without them plugged in and observing the engines behavior is a way to help diagnose certain issues. I don't know about on these cars/engines, but generally when a MAF is disconnected and the car is ran the ECU reverts to a predetermined parameter (or relies on other sensors input) for air/fuel. Have you tried running the car with the MAF unplugged (I'm also not sure how these engines react to that, ie, if it's a good idea)? But with that being said, it seems to me things are pointing in the MAFS direction. Do you perhaps know someone you can swap with for a quick 10-15 minute drive?

[Hofmeister]

Wow that was quick....lol
Thanks, I looked at the intake boot for signs of cracks and all of the associated lines and didn't see anything obvious???

theres that boot, theres the icv lines running under the intake, theres 2 crank case vent lines and also the felt vapor line into the bottom of the throttle body. Your car can run perfect 99% of the time and still have a vacuum leak, as I just found out mine did.

[will308]

Thanks for all of the responses. You know, things happen for a reason. I bought another e34 about 2 weeks ago for the interior. As luck would have it, it has the same MAF as my car (my car's build date is 6/95, new car is 10/95). I switched the MAFs late this afternoon and so far the car is behaving well. A few things of note,. Maf came out of a 5 speed car but I don't think it mattered? While I was changing things, I did notice quite a bit of oil in the rubber boot just in front of the throttlebody. I don't know if that has anything to do with the issue as it's downwind so to speak of the MAF. To be absolutely sure it's a bad MAF.. I'm gonna hook the old one up to the other car and see what it does.
Thanks again, I have my fingers crossed...

[will308]

OK,
Just wanted to do a final post on the subject. Seems the Peake code reader was correct. I installed the MAF out of the 5 speed car and it's been running fine.
I do have another question...there was, what I consider, a significant amount of motor oil in the intake boot just before the throttle body...would that cause an issue with the original MAF? I have a '91 with a non-vanos motor with 257,000 mile and it has the original MAF ( albeit a different type).
Thanks again for all of the help..
Hofmeister...I am planning on replacing the vac line as the ones on the car seem to be the originals....

[will308]

Well, time to renew this thread...seems the old surging while coming to a stop has reared it's ugly head again.
It really feels like a trans related issue, like the converter is not decoupling correctly or on time, causing the engine to almost cut out ,only to be saved by the decouple at the last second???
Anyone else have this type on an issue?
Thanks,

[cstrazz]

Hello, I am having similiar issues. I just replaced the air intake boot and hoses. Maybe a bad Mass Airflow? Please let me know. My car is a 5-speed transmission.

[will308]

Hello, I am having similiar issues. I just replaced the air intake boot and hoses. Maybe a bad Mass Airflow? Please let me know. My car is a 5-speed transmission.

I haven't been driving my car that has this issue. I recently bought another '95 525 w/automatic and it does not have this problem. I'm surprised that your car has it as it's a 5 speed...assuming a manual. I'll begin driving that car when salt clears off the roads here in Maryland in the spring. I'll follow up then.

[bolloc]

I know diddly squat about MAF's however the interesting point I picked up in these posts was oil in the intake boot. My thought was if the MAF does what the name implies then perhaps sucking oil into it may affect the sensing which would result in bogus info being sent to the computer... I looked up how a MAF works, and yes oil will affect it. Having said that perhaps the MAF on these cars work differently and are not affected. Hopefully someone more knowledgeable will jump in and verify or set me straight.

So in my opinion, this is cause and effect, you have oil in the intake which shouldn't be there, which causes erroneous sensor readings that were nullified by replacing the MAF until the replacement was either contaminated to a similar degree or ruined. The auto transmission was also a cause and effect, the motor is acting weird so the transmission 'feel' was different.

[gtopaul]

I know diddly squat about MAF's however the interesting point I picked up in these posts was oil in the intake boot. My thought was if the MAF does what the name implies then perhaps sucking oil into it may affect the sensing which would result in bogus info being sent to the computer... I looked up how a MAF works, and yes oil will affect it. Having said that perhaps the MAF on these cars work differently and are not affected. Hopefully someone more knowledgeable will jump in and verify or set me straight.

So in my opinion, this is cause and effect, you have oil in the intake which shouldn't be there, which causes erroneous sensor readings that were nullified by replacing the MAF until the replacement was either contaminated to a similar degree or ruined. The auto transmission was also a cause and effect, the motor is acting weird so the transmission 'feel' was different.

The oil is getting into the intake boot past the MAF so it wouldn't get into the MAF. The oil comes from the crankcase vent hose which plugs in under the intake boot on the right side. Not totally uncommon to see a little puddle of oil there in the intake boot but no way it would get into the MAF. I had a similar problem last fall with the check engine light coming on and the car wanting to die. Scan read intake temp sensor and MAF. I replaced the temp sensor and used two different, new, MAFs and still had the problem. Appeared to be worse on cold starts but off idle ran ok. Called a retired BMW master tech friend of mine and he said run a can of 44K through it. (We used to do this at the dealership as part of the Inspection I and II process.) I added the can of 44k to the gas and took it on a 30 minute drive and have never had the problem again. 44k is a bit pricey at over $20 a can but it frees up the rings which can cause rough idle and other problems. Will be adding a can to my M5 too as a preventive measure. It worked for me.;)

[bolloc]

Thanks for the clarification...

I have always been somewhat sceptical about using additives that claim to clean, did a quick search on 44k and it does seem to have a lot of positive reviews with regards to cleaning the fuel system. In fact I wouldn't be surprised if it actually works because it doesn't appear to be available here (Ontario) - government policy is if a chemical is good, ban it.

[will308]

You know, while thinking about this, my 1991 525i did a similar thing, many years ago ( I've owned it since 12/90). I ended up replacing the hose under the intake manifold that connects to the ICV. There was an updated version and once that was replaced...no isuues.
My new (just picked it up in November,'14) '95, 525i also has an auto and it doesn't have this issue? The only difference is the newer car has traction control and the intake boots are not the same?
I wonder if that has anything to do with it?
And yes the little puddle of oil is downstream of the MAF so it's unlikely the oil is affecting it?
Thanks for all of the responses to this perplexing problem...