Hi. I've become quite intimate with my vacuum system. Yet I have a leak and I cannot locate the exact source.
Removing all other systems and testing both the pump and the brake booster - I'm confident this is within the locks, and unrelated to climate, shutoff, VCV, etc.
I've also tested the lines branching off from the driver's floor to the rest of the doors, trunk, and gas lid. We're good there, and I've tested the storage tank too.
I've isolated the vacuum leak to somewhere between the driver's door master element, and the yellow splitter/check valve on the other side of the firewall. I've been inside my door and tested the master element. I've tested the yellow check valve. Both are fine.
When i shut off my car, there is a clear whine (that I have confirmed is directly connected to the leak) that seems to come from somewhere behind the dash/kick/cluster area. If I quickly lock the car, the whine stops, and I have plenty of vacuum stored to unlock the car an hour later. When idling with no radio noise, you can also hear this whine. When I remove the lock branch from within the engine bay, the whine is gone.
this diagram indicates a check valve somewhere in the dash area, after the yellow splitter valve in the engine bay, and before the door elements.
I believe this is where the leak/whine may be coming from - but I CAN'T SEEM TO FIND THE DANG THING. It's very hard to see with all of the wiring and cabling stuff up behind the dash, and I just cannot begin to guess where this thing is hidden. Has anybody every located this secret check valve? Forgot to mention, this is an 1982 300D turbo.