When my wife was driving the car regularly, I came home to find the car idling in the driveway. I asked if she was going somewhere and she said, “no, it does that some times and it eventually shuts off”. I suspect that it was merely because the leak at that time was in the door lock actuators and they leak more while unlocked than locked if the boot has a hole in it. (or maybe it was the other way around? Whichever it was, she figured it out and didn’t tell me there was a problem.) I now drive the car and disconnected the doors from the vacuum system in the driver’s footwell (and plugged the source tubes) until I get a chance to do the repair.

In any event, it sounds like you have a small intermittent leak (the worst kind). That small leak will most likely get bigger and more regular until it won’t shut off at all, ever. It’s repair time or isolation time if you can live without the leaking device.

Gobble, Gobble!
Happy Thanksgiving

JohnM 1983 240D 160K 4 sp manual