When a MAF is used in conjunction with an exhaust gas oxygen sensor,
the engine's air/fuel ratio can be controlled very accurately. The
MAF sensor provides the open loop predicted air flow information (the
measured air flow) to the engine's ECU, and the EGO sensor provides
closed loop feedback in order to make minor corrections to the
predicted air mass. Common drawbacks of the widely used hot wire MAF
sensor include high cost and sensor degradation resulting from oil
and dirt build-up degrading sensor accuracy.
When a MAF sensor gets contaminated, it skews the transfer function
such that the MAF overestimates airflow at idle (causes the fuel
system to go rich) and underestimates airflow at high airflow (causes
the fuel system to go lean).