Air flow meter (or mass airflow sensor) is a sensor that is used to measure the amount of air flowing into the vehicles air intake. The information provided by this sensor helps the ECU (engine control unit) in delivering the proper mix of air-fuel mixture to the engine. A defective air flow meter will cause rough idling and loss of power. Two common types of air flow meters are used on automobiles, the hot wire and the vane meter.
Hot wire sensors work by heating a thin wire suspended directly in an air intake system. The air flowing through the wire makes it cooler, and also lowers its electrical resistance. This variation of resistance corresponds to change in voltage signal which is sent back to the ECU.
Vane meter is mounted by projecting a spring-loaded paddle directly into the engine's air intake. Unlike the hot wire type, the air flowing through the vane moves the paddle proportionally. This movement causes the voltage to vary, which is measured and sent back to the ECU.
Both type of air flow meters are sensitive electronic sensors. They need to be cleaned once in a while with electronic contact cleaner. Dirty air flow sensors will decrease your gas mileage and may shorten the life of your engine.