1990-1992 m104 engines 300ce

[e320 coupe]

Is there supposed to be a vacuum line coming from/to the throttle body that is mounted on the intake manifold? I was looking down at the throttle body (I think its the throttle body--the part mounted directly atop the intake manifold and connected to the air filter box) and I noticed a thin line coming from the part. It looks like a vacuum line should be attached to it, but I dont have anything attached to it. So, do you guys know if a line is supposed to be connected there?

thanks for all of 'your' help so far
a.e.b.