Also encountering problems on my 650i, which has now been diagnosed as a valvetronics issue...
Engine Warning Light came on
Took to Garage who repaired the diaphragm breathers
Engine Warning Light re-appeared
Took to BMW specialist
Told me faulty battery – replaced battery
Also changed the oil and pollen filters and replaced the shock absorbers
Engine Warning Light 3rd time…
Returned car to Amari Preston, UK (where bought car from)
Repaired faulty wiring test drove car and told me no problems
Next day - Engine Warning Light re-appeared – car went into Limp mode…
Took car to BM specialist
Their auto-electrician downloaded a load of software and re-calibrated the engine & PDL system which took car out of limp mode and the engine warning light.
Next day...engine warning light and limp mode.
Fault code came up with a faulty battery lead – replaced lead and IBS lead
2 days later - engine warning light and limp mode.
Took back to BMW specialist
Fault code now says problem with the valvetronics