85 300TD

I was replacing the rubber vac lines today, car does not really want to shut off and door locks dont work, and came across a "Pressure Converter Valve". I only know the name because I searched the part number, 001 540 74 97, on allparts.

I did a search and found nothing.. I am guessing it's known as something else but I have no idea. I would like to know what its really called, what it does and how to test it.

Currently I have some hard shifting and perhaps the turbo is inop.

Thanks

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D