Typical idle manifold vacuum varies among engines, and the two biggest factors are valve overlap and idle speed. Also, the same engine with a manual transmission idling in neutral will usually have higher idle speed and vacuum than an automatic idling in Drive, and automatics should always be measured idling in Drive.

The lowest manifold vacuum I have ever seen on a heathy production engine is 10" @ 900 on the '64-'65 Corvette 365/375(FI) horsepower 327s that have the huge "30-30 cam" that is probably the longerst duration, highest overlap cam even installed in a production engine. They're high rev screamers, but a pretty soggy below 3000 even with the aggressive OE spark advance map that gets all the WOT advance in at 2350.

In that same era the 250/300 HP 327s, which had a short duration low overlap cams for stump-pulling low end torque idled at 18-19" @ 500 in Neutral with a manual trans. (In case you rwondering those ratings were "SAE gross", which were probably overated by at least ten ten percent, so take that away and another 10-15 percent to get the modern "SAE net".)

Many Mercedes engines are high output and have fairly long duration and overlap cams, particularly the inline sixes, so they will usually show lower idle vacuum than a typical big displacement V8 that has lower specific output.

My 190E 2.6 five-speed idles at 15" @ 700 in neutral, and it has recently been reported in another thread from "James Dean" that his automatic is 12-13" @ 550 in Drive.

Given that the C36 has a high specific output engine I would expect it to show relatively low idle vacuum, but you need to specify the idle speed - in neutral if a manual and in Drive with an auto.

Reporting idle vacuum without full context as specified above doesn't mean anything.

Duke