Check your battery, it may be nearly dead and not providing enough voltage. The engine will run without electricity on that car, and will shut off, too.

Also, if the battery will charge, it's very likely you have a bad voltage regulator or bad brushes in the alternator -- it comes out (2 screws) with the alternator in the car, from underneath.

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!