I think you mean the Vacuum Control Valve - the modulator is on the tranny itself.
I'm working through this whole thing myself, trying not to have to buy one. I haven't been able to figure out the issue yet....my VCV drops the vacuum, but I'm feeding it 21 and it will drop it to about 8 or so. Too much vacuum. I don't want to spend the money on a VCV if that's not the culprit.
My system is so simple ('81 240D auto) - it goes from the booster vac line up to the switchover valves and down to the VCV - where is it suppose to get dropped down to the 15 in. for the VCV to work with? I get a constant 21??

BTW - I was quoted $157 (MB part) from Caliber Motors in Orange County.

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