Mass Airflow Sensor
The mass airflow sensor is located between the air filter and the throttle plates(3). All engine air is drawn through the mass airflow sensor. The sensor consists of a tunnel containing a airflow measuring device and a dampening flap, which are offset 90 degrees on the same casting. The measuring flap swings in the air stream against the pressure of a spiral spring and is connected to a potentiometer. The potentiometer transmits an electrical signal, determined by the measuring flap angle, to inform the ECM of engine load. See Fig 1 .
In addition to monitoring airflow, the sensor also controls the fuel pump operation and engine idle. At idle, the measuring flap is almost closed due to spiral spring pressure. Therefore, an idle air by-pass receives air from the main airflow passage through a small hole, the size of which is controlled by the idle mixture screw. This adjustable air by-pass influences CO levels at low engine speeds.