Uhm....The 4.8i engine as used in the E70 is the N62B48. As such, it employs valvetronic technology for throttle functions. Hence, the conventional butterfly throttle valve is a backup system that normally remains wide open during engine operation. In the event the valvetronic system should fail, the conventional butterfly will provide throttle functions.

So, cleaning the butterfly throttle valve should have no affect on engine performance.

I am sure someone will correct me if I have this wrong.