06 BMW 330i vaccum leak?

I need help finding out why my 330i revs slightly, when I press the brakes in park then after about 40 seconds it revs back down to normal while I'm still holding the brake pedal down , this started happening after I replaced the starter I had to remove the intake manifold to get to it .also it runs rough until I unplugged the maf sensor it ran way smoother

I have noticed the same situation with my 06 325i. 160xxx

Smoke test.

Originally Posted by Chris_a7x

I need help finding out why my 330i revs slightly, when I press the brakes in park then after about 40 seconds it revs back down to normal while I'm still holding the brake pedal down [should be irrelevant] , this started happening after I replaced the starter I had to remove the intake manifold to get to it. [CLUE #1]also it runs rough until I unplugged the maf sensor it ran way smoother [CLUE #2 ]

AFAIK, ALL N52 engine vehicles (330i/xi, 325i/xi, 328i/xi) have a mechanical vacuum pump, driven off the timing chain, which supplies vacuum to the brake booster, and NO connection of the brake booster to the intake manifold. This is due to the VVT throttle system that makes intake manifold vacuum LESS available in many situations. Here is TIS Vacuum hose replacement Procedure, showing pump position:
https://www.newtis.info/tisv2/a/en/e...-servo/I2XH9Ja

Bentley, p.100-8, pdf p.145:

Valvetronic engine load control requires a wide open throttle under
most engine operating conditions, resulting in minimal intake
manifold vacuum. In order to operate the brake vacuum booster, an
auxiliary vacuum pump is fitted to the engine.

Bentley seems to suggest that the Vacuum Pump is "Auxiliary" or supplemental to intake vacuum, but I don't see any vacuum hose other than pump hose (hard plastic) going to booster (NO - T ;-).

So I can't account for any reason that applying brake would affect idle speed, and would assume that what you are experiencing is related to throttle position (try coming to a stop in your driveway using ONLY Handbrake to test).

The other two "CLUES" clearly suggest a vacuum leak. More likely a cracked or loose hose connected to the Intake than the gaskets or loose fasteners, particularly if original hoses. Try spraying Ether/ Starting Fluid on COLD engine hoses under & at rear of intake manifold while COLD engine idles, to see if any idle speed increase, which should occur when cracked hose is sprayed at a particular point.

George

Thank you for the help I'll update when I finish these tests