The mass air flow sensor is located right after a car's air filter along the intake pipe before the engine. The sensor helps a car's computer determine how much fuel and spark the engine should be outputting.
The sensor measures the amount of air coming into the intake pipe using an electrically charged wire. Faulty mass air flow sensors can cause the car to have a rough idle, have bad fuel mileage or cause it to stall. A faulty sensor can sometimes cause a car's check engine light to come on. Regular maintenance through cleaning or replacing the air filter can prevent a faulty sensor.