Check the condition of the idle control valve hoses. If they are hard instead of flexible, replace them and clean the idle control valve with carb cleaner or brake parts cleaner.

Check the condition of all the rest of the rubber bits on the vac lines, too, replace any that are at all not perfect.

If you indeed have a strong vac in the tank -- do you have to pull the filler cap off, or does it vent as soon as you turn it? -- you have a plugged evapration control system vent line. It's under the car someplace near the tank, rubber hose ending in a valve assembly of some sort. Nice place for spiders or etc to build nests.

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!