When the engine is first started, the mixture will be in open loop control mode (fixed) and the idle control valve will be wide open. Once the engine starts, when warm, the mixture control mode will go to closed loop (controlled by oxygen sensor input) and the idle control valve will close momentarily to slow the engine down.

If the mxiture is too lean, the engine will promptly stall -- hence suspicion of a vac leak -- and if the idle control valve is sticky, it won't open up again fast enough to prevent a stall, worse if there is also a vac leak.

Does it occasionally stall when coming to a stop, particularly a rapid one? If so, sticky idle control valve for sure.

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!