I had the same problem with the 300TE when I got it three years ago, fixed it with replacement of said hoses and all the vac line connectors.

Still have a rough idle, but that is the serpentine belt slipping and grabbing, going to fix that on Monday I hope.

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!