If the vac retard diaphram is gone, or the hose leaking or loose, the idle speed will also increase. Won't run badly, just faster.

To set the idle speed, get the engine to operating temp, attach a tach to the coil (electronic one, that is!), and adjust screw to 800 rpm.

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!