Thanks to both of you. I'll try the diagnostic hose swapping over the weekend. This "feels" like a valve problem since all othe vacuum systems are fine. Sloemoe, access looks tight. I didn't find a procedure for this in any of my references (then again I haven't looked real hard). Two questions; Is this a rebuildable valve (o-ring kit, diaphrams etc.) or just replace it? Either way, is it possible to remove the assembly without removing what looks to be most of the manifold assembly etc. A quick walk thorugh of how you did this would be appreciated. Thanks,

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Bart

2002 ML500, 2009 CLK350 Cabriolet
93 300D 2.5 Turbo 265,000 Miles (Sold - bad idea)