P0102 & Bouncing Revs on Cold When Braking

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Ruofdez
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P0102 & Bouncing Revs on Cold When Braking

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.
'03 Z4 3.0i

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Smartbear
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P0102 & Bouncing Revs on Cold When Braking

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 :thumbsup:
Rob
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e89 Sdrive2.0 20i, plenty of mumbo & good economy-the thinking bears z4 :P
e89 Sdrive30i this ones busted, pass me another...
e85 3.0si, i foolishly sold my trouble free car...

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ph001
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P0102 & Bouncing Revs on Cold When Braking

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

This is the hose that commonly splits on the 3.0l....
split elbow.jpg
split elbow.jpg (103.57 KiB) Viewed 68 times
2007 E85 Z4 3.0Si manual :driving:
19" CSL's | Eibach Springs | Aeroskirts | Z4M front bumper | Clear brake light | ZHP | RCH+| Stubby

2004 E46 M3 coupe manual.

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Ruofdez
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P0102 & Bouncing Revs on Cold When Braking

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 :thumbsup:
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.
'03 Z4 3.0i

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P0102 & Bouncing Revs on Cold When Braking

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 :thumbsup:
'03 Z4 3.0i

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ph001
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P0102 & Bouncing Revs on Cold When Braking

Post by ph001 » Tue May 21, 2019 9:21 pm

:thumbsup:
2007 E85 Z4 3.0Si manual :driving:
19" CSL's | Eibach Springs | Aeroskirts | Z4M front bumper | Clear brake light | ZHP | RCH+| Stubby

2004 E46 M3 coupe manual.

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