Impac

Hey everyone i have a problem, has anyone expirianced that and how was the problem solved.
My car 2008 BMW E60 535i im getting a servotronic malfunction on my Idrive mostly under hard acceleration, long story short i took it to the dealer was told p/s fluid needs to be flashed, needs new p/s reservoir, p/s Pump, and p/s rack took it to one shop they replaced the reservoir and pump, no change still thesame problem, toom the car to a second shop they replaced reservoir, pump, rack and flashed the system no change Servotronic Malfunction comes back, car looses power and no p/s at all, what else there can be that i would need to look into ?
I dont have the fault codes since i have not had the car for over a month its been from one shops to another.