I presume that they are refering to the vacuum proportioning valve. This is the device that taylors the constant vacuum of the engines vacuum pump into a vacuum signal that resembles a gas motor (zero at full throttle to 15 inches at idles or there abouts).

I hope they diagnosed all this as there should be no reason to replace either unless something is wrong.


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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician