You probably have more vac leaks that that, though -- usually a leaking climate control isn't enough to wipe out the shutoff.

Check ALL the rubber connectors on the vac lines in the engine compartment. Likely most of them are hard and brittle, which means they are leaking. You can either buy actual MB replacements or just get some appropriate sized vacuum hose and cut pieces to replace.

Check for plugging in the fittings, too, but DO NOT ream them out. The ones on the main vac line for the 617 have precision orifices, and you will have trouble it you widen the opening.

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!