There is also another possibility if the pump proves to be OK. There is a crimp connection in the wires that feeds the vacume pump that runs under the carpet and pad located on the floor where the right rear passengers feet would rest. These wires corrode usually because water got into the car because the sun roof or windows were at one time or another left open during a rain storm. The water remains under the rubber pad and carpet and takes eons to evaporate thus corroding the wire connector located there.
To access the connector remove the carpet trim at the rear door and lift carpet and rubber pad. .. along with rear seat. But before you do all this make sure the fuse you are talking about controlls the vacume pump.
1993 190E 2.3
2000 Toyota 4x4 Tundra