If the car is otherwise running OK, it is probably the shutoff (vacuum)solenoid mentioned above. If you have a mityvac, apply vacuum to the shutoff vacuum fitting atop the injection pump. If the lever actuates and vacuum pressure holds, then the problem lays elsewhere. This is the most common source of your problem, though, and is an easy DIY repair.
\'87 Mer-B 300D (220,000 miles) (sold)
\'93 Mer-B 300D (173,000 miles) (sold)
\'87 Porsche 928 (101,000 miles)
\'98 Dodge Ram quad-cab (250,000 miles)
\'2001 CLK430 Cabrio (50,000 miles)
Past cars: 1969 mercedes 250, 1981 300D, 1972 220D