Mateo sorry to hear of your troubles, I suspect it will be a failing MAF sensor, this senses the air flow and is done by a wire with current running through it measuring the air flow as its current fluctuates as more air being drawn cools it. They are known to be problematic on this engine. Or it could possibly be one of the exhaust sensors, but unlikely to stop it starting.

Look at this site it's a mine of info on these BMW V8 Engines

Adrian

Buggered Off, to a modern none leaky car, heart's still ticking