So my E46 Coupe has a poltergeist in the works. Ive taken it to 2 mechanics and they are dumbfounded. Usually at night, with the electrics loaded up (lights, cruise control, stereo, heater on) there will be a sudden drop in rpm and the battery light will come on for a split second. Recently this has worsened, to the point that the rpms keeping dropping until the engine cuts out. Last night after driving for 30 mins, I pulled over to use the phone and the engine cut out at idle.
The alternator produces a loud whining noise when the car is started cold but this goes away when its warm and the a mechanic checked the alternators output and it was fine.
If anyone could shed any light on this I would be extremely gratetful. I can see me paying a lot of money for people to try and diagnose the issue without any success.