Pyro:

Maybe a plugged tank vent? Algae? Usually algae will cause a serious loss of power, but vacuum in the tank (or possibly bad suction side hoses) can result in fuel starvation at idle, when the feed pump isn't going very fast. Try taking the fuel tank cap off after a hard run and see if air sucks into the tank. If so, the vent line is plugged -- hard to find, it's under the car somewhere near the rear suspension.

It is also possible that you have a bunch of junk in the tank that packs down on the "sock" filter in the tank at speed, and falls back off when you shut the car off.

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!