I am not discouraged because every wrong attempt discarded is a step forward.
A little Experiment
When my idle got soo bad it was making the car rev up and down, it made me aware that this became a sensor problem. I unplugged my Air mass sensor to see what would happen. Lo and Behold the idle smoothed out, I still had an odd hesitation. A new fuel pressure regulator solved this, please remember to use a BMW FPR, an aftermarket will not work and will most likely cause an engine code.