Check the throttle linkage, sounds as if something is a drift.

Otherwise, find a used injection pump, the governor is shot.

Did the PO just change the vacuum shutoff on the injection pump? If so, remove it and verify that it is connected to the internal linkage correctly, if not the engine can run away.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!