P0102 & Bouncing Revs on Cold When Braking

[Ruofdez]

Had quite a good search but struggling to narrow this one down. Since I got the car a couple of months ago it has a P0102 code (Mass or Volume Air Flor A Circuit Low). On cold start if you press the brake pedal the revs bounce between 800rpm and 1200rpm just for a minute or so and then it seems totally fine, though this is my first Z4, so it's possible I'm not picking up something subtle; fuel economy is fine though.

Anyway I'm assuming the code and this behaviour is linked as I've tried resetting the code and it returns quickly.

Because the issue seems to be when pressing the brake pedal I thought it unlikely to be the MAF however I found two threads where people had the exact same symptoms (https://z4-forum.com/forum/viewtopic.php?f=3&t=101186&hilit=manifold and https://z4-forum.com/forum/viewtopic.php?f=3&t=47994) and it sorted it out, so I switched out the MAF for another genuine BMW one (used), but unfortunately no change.

Unplugging the MAF completely seems to result in it running worse but doesn't remove the issue of the revs bouncing, so think I've ruled out both MAFs being bad.

Vacuum leak seems to be a popular suggestion though not sure the best way to check this. Any ideas/advice would be really appreciated.

 

[Smartbear]

Hi, the inlet piping commonly splits on the small elbow close to the throttle body-it’s a diy job to replace
Rob

 

[ph001]

This is the hose that commonly splits on the 3.0l....

 

[Ruofdez]

Hi, the inlet piping commonly splits on the small elbow close to the throttle body-it’s a diy job to replace
Rob

This is the hose that commonly splits on the 3.0l....

split elbow.jpg

That's really helpful, thank you both. I'll have a look and see if that's what's happened.

 

[Ruofdez]

This is the hose that commonly splits on the 3.0l....

split elbow.jpg

You were both spot on. This has split so got one on order. Hopefully it will sort the issue and code

 

[ph001]

 

[Ruofdez]

I replaced this but unfortunately it hasn’t fixed the issue. Does anyone have any more ideas?

 

[ph001]

New MAF has to be next thing to try.

 

[Ruofdez]

New MAF has to be next thing to try.

Already tried swapping the maf with another and no change annoyingly, unless both are bad but seems unlikely?

 

[ph001]

Where did the other used MAF come from? I just can't see this being anything else other than split hose or MAF.

 

[Ruofdez]

Where did the other used MAF come from? I just can't see this being anything else other than split hose or MAF.

Fair enough. eBay. A reputable seller with decent feedback, not just a private one and a genuine BMW part however it is used so you could well be right.

A new MAF is pretty expensive. Is there a way to diagnose the current one either at a dealer or I see the software INPA get mentioned a fair bit?

 

[ph001]

Worth asking bmw what the returns policy is and if there is a restocking charge. I never had any luck measuring airflow in INPA for some reason and others have found the same... see here towards btm of first page.

https://z4-forum.com/forum/viewtopic.php?f=3&t=110050&hilit=inpa


I still think it would be worth running inpa though and comparing the reference values on that thread. Bear in mind that is an N52 though!

 

[Ruofdez]

Worth asking bmw what the returns policy is and if there is a restocking charge. I never had any luck measuring airflow in INPA for some reason and others have found the same... see here towards btm of first page.

https://z4-forum.com/forum/viewtopic.php?f=3&t=110050&hilit=inpa


I still think it would be worth running inpa though and comparing the reference values on that thread. Bear in mind that is an N52 though!

Cheers, I'll have a word with my local BMW garage and see what they say about returns and hopefully only investigate with INPA if there's no joy with that

 

[ph001]

Hi, any update on this?

 

[Ruofdez]

Hi, any update on this?

Unfortunately not. Had to get 4 new tyres, bushes and wheel alignment so funds are running low. It’s next on the to do list but won’t be able to look at it for a few weeks. I’ll keep the thread updated though.

 

[Ruofdez]

Meine luftmasse ist kaputt!



So that's eliminated any doubt. I managed to buy a duff replacement on eBay, doh! I'm now the proud owner of two broken genuine MAFs :lol:

 

[1000rr]

Mine was doing exactly this last week, looking at live values, the maf stayed at 0% irrespective of what throttle position was at. It’s either split I take pipes, a brake servo pipe ( easy to diagnose though, by pumping the brake with engine off or smoke test) or Maf.

I took mine to a BMW Indy this week explaining my MAF was fooked, so could he order another same day, he said 100% it wasn’t MAF, and after telling him it was 100% the MAF and that I looked at the values, no split pipes etc... he still wasn’t having it. Got a phone call apologising that it was indeed the MAF. :headbang:

New Lucas MAF and it’s sorted

 

[Ruofdez]

Mine was doing exactly this last week, looking at live values, the maf stayed at 0% irrespective of what throttle position was at. It’s either split I take pipes, a brake servo pipe ( easy to diagnose though, by pumping the brake with engine off or smoke test) or Maf.

I took mine to a BMW Indy this week explaining my MAF was fooked, so could he order another same day, he said 100% it wasn’t MAF, and after telling him it was 100% the MAF and that I looked at the values, no split pipes etc... he still wasn’t having it. Got a phone call apologising that it was indeed the MAF. :headbang:

New Lucas MAF and it’s sorted

Good you got it sorted, even if he didn't want to believe you! How much did you pay for the MAF?

 

[1000rr]

£83 + VAT for a Lucas one from local supplier.... didn’t want to get a cheap eBay one.

 

[Ruofdez]

£83 + VAT for a Lucas one from local supplier.... didn’t want to get a cheap eBay one.

That’s a bit of a bargain compared to the genuine ones. Don’t suppose you would mind letting me know the part number? Would like to try and find the same one but keep finding the 3 pin one rather than the 5/6 pin.