722.315: Vacuum... again

[CDTurbo001]

Just spent 2 hours going over, and going back over, the vacuum lines and appliances on my turbo coupe. I checked the line pressure the other night (Bowden cable had slack, modulator unhooked - ran it at idle and at 50 km/h, same pressure) and found it at 5 bar, which I adjusted back very close to the spec'd 2.9. It shifted smoother but first gear still wouldn't tolerate much power off idle and the other shifts (except 3-4) were spongy and would borderline slip under heavy throttle - okay, maybe I just need to bump pressure back up a little. But this evening while letting the engine oil drain I went back over the VCV, line routing between all the tees, and the thing connected to the throttle linkages on top of the valve cover (what the heck is that thing?). Upon firing it back up and testing vacuum on the VCV output to the modulator, I had about 15.5 hg at idle, but as soon as the throttle linkage moved it dropped to zero because of the thing on the valve cover dumping all the vacuum. After disconnecting the valve cover thingy and plugging all pertinent fittings I had gradually decreasing vacuum (the way it's supposed to be... right?) from the VCV as the throttle opened so I hooked it up and went for a drive. Slipping like crazy in every gear except 4th. I parked it and called it a day.

The modulator is supposed to have a variable vacuum signal which, in turn, ups line pressure to prevent slippage, right? So what's the explanation for the transmission behaving so awful when it does have that varying vacuum signal? Is the thing on the valve cover supposed to drop all vacuum as soon as the engine comes off idle?