BMW E38 750 M73 V12 runs badly
Why does one cylinder bank of the M73 V12 drop out?
The most common cause is the ignition: a worn distributor cap or rotor, a broken coil or a wiring fault. If the ignition is missing, the injectors do not open on that side. An intake leak does not usually make a bank drop out. Check the ignition first, then the inductive sensor and the fuel.
How do you read the M73 fault codes?
Each cylinder bank has its own control unit. Reading only the first bank does not show the second bank's codes, so read both. Unplugging one control box helps find out which side the fault is on.
What else causes an uneven idle or vibration?
Replace worn distributor caps and rotors and check the ignition leads. The M73 leads do not fit the M70, nor the other way around. Suitable spark plugs are Bosch F9LCR2 or NGK ZFR5F; a four-electrode plug does not fit. A dirty mass air flow sensor is cleaned only with brake cleaner, not oil.
Can a vibration when running cold have a cause other than the ignition?
Yes. The air pump feeds air into the exhaust manifolds, and a burnt pump resistor made cylinders 1 and 2 run lean when cold. A compression test reveals a head gasket leak when the cylinders leak pressure into each other.