Idle Air valve control on 2000 BMW Z3

Suddenly my idle air valve control went bad!
What is the common reason for this to go bad?
Also, approximately how much should it cost if I take it in to a shop?
Thank you,

1 answer 1 comment
The idle air control motor takes about an hour to change and the part is about $185. Carbon build up normally causes the slider in the air control motor to bind up, on some cars you can just clean them.
Hi, would this problem cause the car to back fire and kill revs, there is a buzzing noise coming from a black box top and centre of the engine is that the part being discussed.
Regards
Jack