Weird vacuum problem

[CPTON]

Background:

Ok so my car (95 318is) dies sometimes i can start it up after and make it idle with the gas pedal for about 30 seconds then its usually good to idle by itself. Driving there is no problem but it will just stall sometimes when i depress the clutch to stop.


So one day i was pumping the gas pedal while idling and the rpms went up, i read on here that this is apparently normal because there is a vacuum line going to the brake master cylinder.

Anyways the other day i pumped them again and the car began to stumble and kind of pop a bit, like it was choking.

So i tested my girlfriends car (mazda precidia) and her car stumbles a little too when pumping the brakes.


So i looked for vacuum leaks couldnt visually see any, so i tried spraying some water around, didnt notice anything but i didnt like spraying it near the alternator and pulleys so i tried the propane. I pulled a small vacuum hose from the intake manifold and it made the car idle higher but still steady, then i let some propane get sucked in through that hose (so i could tell what would happen if there was a vacuum leak) and nothing changed. So i reved it while lettting the propane flow and nothing even tried it around the air filter.

So whats a good way to test for vacuum leaks and what is normal for the car to stumble or idle higher when pumping the brakes?

Thanks

[Wayne 962]

I like to use carb cleaner - usually works for me. But, it only works for intake manifold vacuum, not crankcase manifold vacuum. The intake vacuum gets sucked into the intake (and makes the engine rev), but the crankcase vacuum simply gets sucked into the crankcase...

If you pull hoses, and the idle doesn't change, then that is a sign that there is a vacuum leak. Check the big intake boot - these crack all the time and are difficult to see from all angles while installed on the car...

-Wayne