My friend and mechanical guru Steve tells this story concerning my 81 240d when the PO still owned it.
Seems the PO called Steve one evening to say that the car wouldn't shut off and could he come over and take a look at it to see if he can fix it.
He gets over there a bit later and sure enough he finds the car idling in the drive. He asked the PO when this happened and the PO replied...
a week ago! LOL
Steve can't remember how he stopped it, being unaware of MB vacuum systems ; but he managed it somehow.
This was many years ago and the car is none the worse for it.

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1981 240D 143k 4 spd manual -SOLD

2004 VW Jetta TDI 5 speed 300k -still driven daily