These have been a long issues on the petrols. However they were a lot easier to change as they sat on the engine valve cover.
Bmw decided to put it inside the bloody engine.
Essentially it controls the valve lift and the camshafts only carry out timing. If the motor is as min then the valves hardly open, if it's at max it's open fully. They work together for better performance and fuel economy. The throttle body is always open and the throttle/revs in controlled by the valvetronic - that's what I've read anyway.
So any starting, throttle issues combined with clicking noises coming from the engine is likely that motor.
This is mine:
Clicking - as the motor turns back to start (min)
Rough idle -