[RadSavage]

I know there’s already a lot of threads about coils and idling and so on, but I haven’t found anything specific to what I’m experiencing. Apologies in advance if there are and I missed them...

I was recently experiencing the textbook signs of bad coils in my ‘07 328, so I went ahead and replaced all of them as well as the spark plugs. Fired the car up right after I was done, drove around for a bit and everything was great. The next morning I went to start it up, it began revving on its own, so I gave it some gas a couple good times and it seemed to go away. What I have since come to discover is that this happens only when I start the car after it’s been sitting for a while (over night, after work, etc...), and it only happens when I have the brake pedal held down. If I let off the break immediately after pushing the ignition button, it doesn’t happen, but the minute I push on the break to put it in gear, it’ll start doing it unless I let it sit and “warm up” for a few minutes or rev it pretty good myself a couple of times. Again, this is only after it’s been sitting for a while, does not happen once I’m driving, and does go away after a few minutes.

Any pointers will be greatly appreciated.

[e90yyc]

I have an issue similar to yours, but because mine is so minor (slight fluctuations and for a very brief time only) I haven’t spent much time troubleshooting it as there are other issues I’d like to address first. I haven’t noticed any correlation between pressing the brake or not. I will pay more attention in the coming days.

It was suggested to me that perhaps there is a vacuum leak. Admittedly I don’t know much about the vacuum systems in these cars. I know the brake booster works off vacuum (possible link to your issue?) but also know there is a vacuum pump as our engines create insufficient vacuum on their own.

I also know I have an exhaust leak at or near the header. I doubt this would have anything to do with it though.

[rawdog573]

Sounds like the diagram inside your vacuum booster is bad causing a vacuum leak only when the brake is applied. I would go for a new vacuum booster.

[lowrydr310]

Originally Posted by rawdog573

Sounds like the diagram inside your vacuum booster is bad causing a vacuum leak only when the brake is applied. I would go for a new vacuum booster.

The master cylinder brake booster vacuum line on the N52 is NOT connected to the intake manifold like it is on most other cars. Because of the valvetronic system to control throttle, there is very little intake manifold vacuum. The N52 has a standalone vacuum pump for the brake booster. Therefore a vacuum leak is not very likely to cause fluctuations in idle like it would on most other cars.

[RadSavage]

I appreciate you guys putting your heads together on this one. So even with the one saying not likely, that means it’s still could be likely. I think the trickiest part of this equation is that it only happens when it’s been sitting for over let’s say 8 hours..?

[blkE92_ricky]

Hello, looks like this is an old Colin but I can’t find anything else that describes this situation and I’m having the exact thing going on on mine! Only on cold starts if I press the brake I will have a “rpm surge” almost like it wants to stall. Once the car warms up it goes away. I did notice that when I down shift I see a slight drop of rpm’s while I press the brake, I drive it on manual gears most of the time. I checked the hose going from booster to vacuum pump and it looks good no cracks or loose ends. I can’t seem to get any info anywhere about this.

[IzzyE92]

Any updates on this?

I have had this issue where ONLY on cold starts if I press the brakes, the RPMs shoot up and the car acts like it wants to stall. Once warms up, it’s fine.

I have replaced:
Vacuum Pump, Intake Manifold Gasket, Brake Booster, Master Cylinder, Booster Grommet and Check Valve Hose, Valve Cover, Coils and Plugs and can’t find the culprit!

[hoyer801]

Originally Posted by IzzyE92

Any updates on this?

I have had this issue where ONLY on cold starts if I press the brakes, the RPMs shoot up and the car acts like it wants to stall. Once warms up, it’s fine.

I have replaced:
Vacuum Pump, Intake Manifold Gasket, Brake Booster, Master Cylinder, Booster Grommet and Check Valve Hose, Valve Cover, Coils and Plugs and can’t find the culprit!

I'm having the exact same issue and my initial thought was vacuum leak. My daughter also says that in the mornings, she has a very hard time pressing down the brake pedal so it'll start. I've read that's very common, this is why I was thinking brake booster hoses since both tend to only happen when the engine is very cold.

Did you ever end up fixing this?

[Rexhavok]

Originally Posted by hoyer801

I'm having the exact same issue and my initial thought was vacuum leak. My daughter also says that in the mornings, she has a very hard time pressing down the brake pedal so it'll start. I've read that's very common, this is why I was thinking brake booster hoses since both tend to only happen when the engine is very cold.

Did you ever end up fixing this?

BUMP!
I'm in a similar place. Rock hard pedal if it's left for more than 8 hours or so and sometimes pressing the brake makes it feel like there's a misfire going on. I know the brake vacuum system is separate from the intake vacuum but what's the little T fitting on number 14 lead to?
https://www.realoem.com/bmw/enUS/sho...diagId=34_1481

[fastboatster]

Originally Posted by Rexhavok

BUMP!
I'm in a similar place. Rock hard pedal if it's left for more than 8 hours or so and sometimes pressing the brake makes it feel like there's a misfire going on. I know the brake vacuum system is separate from the intake vacuum but what's the little T fitting on number 14 lead to?
https://www.realoem.com/bmw/enUS/sho...diagId=34_1481

Brake vacuum system is not really disconnected from the intake system. Brake vacuum pump does not evacuate the booster to the atmosphere, instead, that air goes into the crankcase and then it gets to the intake via pcv system.
I didn’t check that diagram, but vacuum from the pump is also used to actuate the exhaust flap if your car is equipped with one. If your brake pedal gets rock hard after 8hrs then there’s definitely some brake booster issue.

[Tambohamilton]

Not necessarily brake booster - could be a leak anywhere in the vac system, upstream of the check valve...or the check valve itself.

[fastboatster]

Originally Posted by Tambohamilton

Not necessarily brake booster - could be a leak anywhere in the vac system, upstream of the check valve...or the check valve itself.

check valve is built into the booster, even if the vacuum line is disconnected from the booster, it's still supposed to store vacuum.

[mainbearing]

See this TSB (SI B34 06 07) supposed up to 09/2007. Besides the check valve, a member said the rubber grommet at the booster may be a culprit.

I am starting to have this problem as well and it is becoming more frequent. I might just go ahead and replace the junk plastic pipes and grommet(s) between the vauum pump and the booster and see how it goes.

I think BMW used a lot of unreliable parts on this car, but a shitty booster is not in the picture for now.

https://www.e90post.com/forums/showthread.php?t=589119

[Tambohamilton]

Originally Posted by fastboatster

check valve is built into the booster, even if the vacuum line is disconnected from the booster, it's still supposed to store vacuum.

I did not know that. How come the booster grommet (at the vac hose) causes overnight vacuum loss for some people?

[fastboatster]

Yeah, rubber grommet on the booster might be an issue. I took a look at my old brake booster vacuum hose, looks like the check valve is actually in the part which goes into the booster.
P.S. also, looks like the check valve part on the hose is a little bit more complex than just one check valve, it looks like there’s one check valve which separate the booster from the hose if necessary, but there’s some kind of a valve/diaphragm which slowly allows the air into the hose if there’s too much vacuum. Long story short, I had some vacuum related issues some time ago, ended up being the exhaust valve flap actuator and its solenoid.