Something is not right with your vacuum or it would be shutting off with the key. Could be the shut off valve.

Will the car shut off by depressing the stop lever on the throttle linkage (under the hood)? If not it could be a throttle linkage adjustment problem.

Is the linkage on the back of the pump, at the "stop" (IE: wide open)? Or is it down where it should be (for idle speed)?

Worry about the vacuum later... You need to get the "wide open" problem sorted out first. It sounds like you may need to unhook all of the throttle linkage and work from to pump towards the valve cover to find the problem.

It is possible that the pump itself could be malfunctioning too. But, not enough information at this point....

__________________
AJ

1985 300D (SOLD)