Lots of good info on this thread!

My car shows the proper vacuum at idle while in park (needle all the way to the left), but as soon as I put the car in gear, the needle jumps to 3/4? I'm assuming this isn't normal? Thanks.

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles