BMW E39 mass air flow sensor (MAF) fault and replacement
How does a faulty mass air flow sensor (MAF) show up in an E39 and where do I start diagnosing?
Symptoms are an uneven idle and a warning light that comes on occasionally when the adaptation values are exceeded. First check for intake leaks and the intake duct connections. If the values are still exceeded, the sensor may be the cause. A broken circuit shows up as a fault code. Unplugging the sensor is only a test to locate the fault.
Does cleaning the mass air flow sensor help or does it need replacing?
Cleaning (for example with CRC cleaner, about 20 minutes) has improved operation considerably, but it does not always solve the fault completely. When replacing, use an original Siemens/VDO sensor, because an aftermarket sensor does not always fix the fault or work in the car.
Does a new mass air flow sensor need to be programmed?
With the original part number programming is usually not needed, but with some replacement sensors coding at a dealer has been needed. After replacement the engine control's learned values can be confused: they can be reset with a diagnostic tool or they relearn slowly. Also check the wiring and the connector.