Did you try:
1) Hard iDrive reset: hold power button 20+seconds
2) Hard iPhone reset
3) Removing the car from the phone Bluetooth list and the phone from iDrive bluetooth list and pairing again?
1) Hard iDrive reset: hold power button 20+seconds
2) Hard iPhone reset
3) Removing the car from the phone Bluetooth list and the phone from iDrive bluetooth list and pairing again?