No trigger points on K-Jet, as a '77 280 would be.

Possible that you have a loose or warped intake manifold, too, that opens up and causes a big vac leak with a hot engine -- another poster had this problem in the earlier L6 engine.

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!