1983 300SD vacuum diagnosis

Hi, All,

I have isolated a vacuum problem to the red/green plastic line that services (I think) interior switches and servos: with this red/green line attached to its fitting on the vac system, system pressure drops from 45m/g to 15m/g or less with the engine running. When the car is turned OFF, the line holds vacuum (??); when the car is ON, its as if it's open on the other end, bleeding off vacuum (brakes go hard after 2-3 pumps; engine won't shut off if at idle awhile).

Does this behavior suggest a specific component that I should go after?

Thanks in advance!

Wayne
Annandale VA

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