Whats this wire do?

I need help identifying the function of a wire that runs from the wiring block that sits around the throttle body back toward the engine. It runs in right next to the bracket and nut that holds the intake manifold.



For those of you who require pictures I apologize. I am unable to get close enough for a good pic. Hopefully my description will suffice. If it matters its 2001 325i.



Thanks!