That the ICV goes open with no power.

You need to check for vac leaks -- rubber idle control valve hoses, tranny line, climate control lines, any switchover valve lines, boot between fuel distributor air horn and throttle valve, injector and injector holder seals.

Judicious use of brake parts cleaner or carb cleaner spray aimed at suspect locations will help you diagnose leaks -- a quick squirt that causes the idle to change (almost always smooths out) indicates a vac leak.

If the idle control valve hoses are rock hard, you should relace the boot between fuel distributor air horn and throttle hody as well, it's the same age.

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!