Mass airflow sensors or, more technically, “airflow sensors,” are an integral part of modern import engine management systems. In addition to providing an exact measurement of airflow into the engine, airflow sensor inputs can be used to measure intake air temperature, provide an emergency shut-off for the fuel pump and provide a load-sensing input to the powertrain control module (PCM) to help control the shift points and shift quality of an automatic transmission.

Until airflow sensors were popularly introduced, engine management systems used the throttle sensor, intake air temperature, engine speed and intake manifold absolute pressure (MAP) to calculate (rather than directly measure) the volume of air flowing into an engine. These systems were called “speed density” systems.
In the case of engine management systems using an airflow sensor, airflow is converted directly into a voltage or frequency signal that’s sent to the PCM.  The direct measurement provided by an airflow sensor reduces fuel calculation errors caused by the miscalibration or degradation of the throttle, intake air and manifold absolute pressure sensors...