I do not want to hijack this thread but, I am having similar problems. I have a mighty vac and can check the lines. I have vacuum at the top of the BFS.
1. Does the VCV feed vacuum back to the bottom of the BFS on the VCV line?
2. Until I straighten this out. Can I remove the VCV line at the bottom of the BFS and connect it to the trans and check for vacuum at the modulator and/or make the car more driveable?
3. I'm guessing that line C (ancilliaries) is the climate control, etc. I'm sure I have leaks there, no footwell heat, just dash vents. If this is robbing vacuum from the system would capping line C at the pump help?
4. Does the pressure at the bottom of the BFS come from the manifold thru y30, the ALDA and y29? I have no manifold pressure or vacuum at idle.
Thanks.

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1987 300D 146K Original #14 Head
One eye on the road, the other on the temp. gauge

Gone But Not Forgotten
1983 380 SEL Long gone
1983 300SD Wish I hadn't traded it in on a 90' Corvette
1989 300SE My all time favorite
1995 E420 Went like a bullet