Hi everyone
I know some of you would think of it as weired question, but i'll give it a shot.

Can someone help me and tell me if he/she knows of a site similar to this but for BMW cars?

I have a car that has the following problem, it's a 1992 European BMW 320. The car has the following symptoms:
1) When I start the car, the RPM alternates up and down.
2) If I step on the gas after startup, the RPM goes ok, but if I stop stepping on the gas, the car switches off.

A mechanic told me that there's a piece that needs replacement, I don't know its name, but it controls the amount of air going to the engine. This piece is somewhere between the air filter and the compulsion chamber and has a power cable attached to it to feed a small electrical circuit.

So, anyone has an idea what might causing the problem? And what is the name of the piece I described?

Many thanks
PS: didn't I mention from the beginning it's a strange question