Yes you can test for vacuum going into the VCV (and all prior points)at a standstill. You'll have to test the output of the VCV while driving though, I think since you need to open the rack to see how the VCV responds.

Conceptually what the VCV should be doing is mimicking the behavior of vacuum in a gasoline engine under various load conditions.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
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