Adjust the idle speed on setting higher if you can (some cars don't have the adjuster -- black "wheel" next to the brake booster. Pull out and rotate one notch CCW and see what happens).

If the electronic idle control has failed (check the electrical connections on the IP), you will have unstable idle sometimes. You can manually adjust the idle speed up some to help.

Other that that, a compression check is in order for possible ring leakage. Low compression can lead to crapped up rings, and this will take a while to clear. Use synthetic oil and take a long trip -- does wonders for the idle.

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!