Chances are the cap, rotor, and ignition wires are ancient on this car, as it will run (although badly) with the rotor burned badly and the contacts in the cap burned down to the cap material!

Check for the following:

Any signs of arcing on the plug and coil wires. Any evidence (spiderweb traces, ashy spots, burned insulation), replace wires.

Pull cap (a PITA) and inspect -- likely it will have been toast for some time.

Replace them and it will run much beter.

Also check for a cracked rotor carrier (the bit that bolts to the cranshaft the rotor is screwed onto) -- these are known to break in these cars, and can cause running and starting problems when they slip out of position, then slip again and are close to correct.

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!