Mass Air Flow Sensor
A MAF (Mass Air Flow) sensor measures the volume of air passing through the air tube. There are several types found on vehicles today. These include the cold wire, hot wire, Karmen Vortex, and the vane type MAF sensors. This sensor is also known as an air flow meter.
The vane type uses a paddle or door that moves as the air rushes by. This type of sensor utilizes a potentiometer (variable resister) to send a variable or changing voltage signal to the ECM in proportion to air volume.
The cold wire MAF sensor uses thin metal strips that vibrate as the air passes by. This vibration changes in frequency as does the signal sent to the ECM.
The hot wire MAF sensor has a heated filament like a toaster. The sensors resistance changes or decreases as cool air passes by the filament. The increase in current to maintain the sensors heat is converted to a voltage signal and sent to the ECM to adjust fuel trim.
Because this filament gets dirty from wear, a cleaning may return a hot wire MAF to its normal operating condition. There are many products designed to clean a dirty MAF sensor on the market and the whole process usually only takes a few minutes. Just remove the sensor and spray the filament until it is clean, then just re-install the sensor. Dirty MAF sensor symptoms include loss of power, hesitation and stumble, as well as poor gas mileage.
The Karmen Vortex air flow meter does the same thing as the rest but creates a vortex 
that is sensed by a photo coupler and a mirror. This signal is converted to a voltage signal to be sent and interpreted by the ECM. The sensor in the image is a Karmen Vortex air flow meter.
Most MAF sensors have an internal IAT (Intake Air Temperature) sensor located inside of the sensor. The ECM uses the MAF sensors signal along with temperature and pressure signals to make accurate air fuel adjustments while in open loop. These signals used in correlation with the closed loop signal from the oxygen sensor provide extremely accurate fuel trim conditions (14.7:1) stoichiometry.
The MAF sensor provides the ECM and TCM with valuable information regarding engine load. The transmission control unit uses this information for shift control. A mass air flow sensor left unplugged or in need of cleaning will effect a vehicles shift control dramatically.
