P0102 & Bouncing Revs on Cold When Braking

Ruofdez · Post by **Ruofdez** » Thu May 16, 2019 10:06 am

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 (viewtopic.php?f=3&t=101186&hilit=manifold and 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 · Post by **Smartbear** » Thu May 16, 2019 10:28 am

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

Rob

ph001 · Post by **ph001** » Thu May 16, 2019 11:00 am

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

: split elbow.jpg (103.57 KiB) Viewed 1805 times

Ruofdez · Post by **Ruofdez** » Thu May 16, 2019 12:38 pm

Smartbear wrote: ↑Thu May 16, 2019 10:28 am Hi, the inlet piping commonly splits on the small elbow close to the throttle body-it’s a diy job to replace
Rob

ph001 wrote: ↑Thu May 16, 2019 11:00 am 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 · Post by **Ruofdez** » Tue May 21, 2019 9:09 pm

ph001 wrote: ↑Thu May 16, 2019 11:00 am 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 · Post by **ph001** » Tue May 21, 2019 9:21 pm

Ruofdez · Post by **Ruofdez** » Tue May 28, 2019 11:41 am

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

ph001 · Post by **ph001** » Wed May 29, 2019 12:03 am

New MAF has to be next thing to try.

Ruofdez · Post by **Ruofdez** » Wed May 29, 2019 6:21 am

ph001 wrote: ↑Wed May 29, 2019 12:03 am 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 · Post by **ph001** » Wed May 29, 2019 11:34 pm

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

Ruofdez · Post by **Ruofdez** » Thu May 30, 2019 6:01 am

ph001 wrote: ↑Wed May 29, 2019 11:34 pm 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 · Post by **ph001** » Fri May 31, 2019 10:08 pm

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.

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 · Post by **Ruofdez** » Sun Jun 02, 2019 9:19 pm

ph001 wrote: ↑Fri May 31, 2019 10:08 pm 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.

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 · Post by **ph001** » Mon Jun 10, 2019 8:59 pm

Hi, any update on this?

Ruofdez · Post by **Ruofdez** » Tue Jun 11, 2019 6:33 am

ph001 wrote: ↑Mon Jun 10, 2019 8:59 pm 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.

Z4-forum.com

Z4-forum.com