1994 BMW 525i shuts down by its self

i have 1994 bmw 525i
every thing is good
the only problem is when i drive it and i get on a red light or a stop sign and i stop it shuts down.
so i have to press the gas pedal a little so it wont shut down.
when i drive it, it runs and feels good. It seems that there is no trouble at all.

Can it be the air valve?

thanks