Sweet Jesus is that thing idling fast, this is what I call the first signs of a run away engine....keep a pair of snips close by to cut the fuel line when it starts racing....don't ask me how I know.....

You have a leather diaghram in the rear of the injection pump, this is torn and cause high idle....they can be changed out but there is a little pin that needs to be removed, and yes its one of them cussing screaming kicking the tires type pin..

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Good read
1973 220D W115 Injection Pump Gasket - Benzworld.org - Mercedes-Benz Discussion Forum

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