Error P0102 occuring every time the car runs

[Anonymous]

Hi Everyone,

I have recently purchased my first Z4, its a 3.0 litre and runs perfectly fine, the only issue I am having with it is that when I put my foot on the brake the car will rev up from about 500 to 1000 rpm.
I have replaced the "rubber boot" on the car that is part of the "Hot-film air mass sensor" shown on real OEM as the correlated part of the plastic had split.
http://www.realoem.com/bmw/enUS/showparts?id=BT52-EUR-02-2004-E85-BMW-Z4_30i&diagId=13_0995

Using INPA I read the error code P0102 or 2783 depending on which part you read, but having checked http://www.z4-forum.com/forum/viewtopic.php?t=9444 I can see that P0102 is Mass or Volume Air Flow Circuit Low Input. Like I said, the car runs perfectly fine apart from when I put my foot on the brake it seems to rev higher. I was wondering if anyone else was having any issues with this and could shed some light on why this is happening and if it is related to the brake revving.

 

[ph001]

Sounds very odd. Can you clarify exactly how this is happening?? Do you mean when car is stationery in neutral and you apply the footbrake then the car increases in revs?? 500 rpm sounds a bit low for an idle in the first place.

The brake master cylinder utilises energy in terms of vacuum on the inlet manifold to give you assisted brakes, so applying the brakes must be changing the pressure there somehow (it shouldn't though). I can only image that there is some kind of vacuum leak / split somewhere which is screwing up the idle.

Your P0102 error code would back this up (i.e. air is getting into the inlet but bypassing the air flow meter).

 

[Anonymous]

Sounds very odd. Can you clarify exactly how this is happening?? Do you mean when car is stationery in neutral and you apply the footbrake then the car increases in revs?? 500 rpm sounds a bit low for an idle in the first place.

The brake master cylinder utilises energy in terms of vacuum on the inlet manifold to give you assisted brakes, so applying the brakes must be changing the pressure there somehow (it shouldn't though). I can only image that there is some kind of vacuum leak / split somewhere which is screwing up the idle.

Your P0102 error code would back this up (i.e. air is getting into the inlet but bypassing the air flow meter).

Yeah you've got it right, when I am stationary and I put my foot on the brake then it revs up. The car idles at around 800rpm sorry, and rises to between 1000 and 1200 rpm when the foot is on the brake. As mentioned above, I have fixed one air leak, but am not sure where to start looking if there is another.

 

[andyfanshawe]

Without looking at scan data, this is all guesswork, Not good, but here goes....there is a possibility the one way check valve is not working in the servo. Pull the vacuum pipe off the servo and block it up, and see if shows the same symptoms.
Ideally we need to see short term and long term fuel trims and o2 sensors while it is doing it.

If that was in my workshop, I would smoke the inlet straightaway to eliminate more air leaks.
Whereabouts are you?

Andy.

 

[ph001]

Sorry, I meant servo not master cylinder. Good call on the check valve. The other thing you can try is spraying something like damp start around suspect areas. The revs will increase where it sucks the vapour into the inlet.

 

[Nova2k7]

i had this!! spent years with issue! every time i pressed the break the car would rev itself up to just over 1k.

replaced the MAF and it sorted it straight away, part was about £200

 

[ph001]

i had this!! spent years with issue! every time i pressed the break the car would rev itself up to just over 1k.

replaced the MAF and it sorted it straight away, part was about £200

Wow, not the first thing you would suspect. Maybe the op could just disconnect the connector as a check to see if it makes a difference. Did you ever try that out of interest?