I currently drive a 1993 300E and well I have a slight issue with idling. When i'm in neutral or simply waiting at a red light in drive, my car revs on and off on it's own then very rarely even turns off because the rpms become too low. I'm no expert mechanic but I think I might have a vacuume leak? Is this necessairly possible? I tried asking my mechanic but he always likes to see money before he says anything and i'm not so sure I want to pay him just to fix a simple hose. Either way, i'll probiably end up taking it to him, because its too damn cold and i'm lazy plus my bf won't help at all. x__x" ANY WAY Uh basic question i'm trying to ask is,

Why does my car rev while idling/in neutral/at red lights/or in park... Or basically while i'm stopped.
What could be some possible reasons for this to happen?

Thanks for your time.