According to the vaccuum diagram for my 83 300 DT, the black line is a vent into the passenger compartment. Should it be connected to anything in the passenger compartment like a check valve or something? Mine is just hanging and it seems to be the cause of insuffiencient vacuum and a jumpy needle on the MityVac gauge. If I block the line off, the gauge rises to 20" hg, left openm it flutuates between 10 to 15" hg.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
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