An air flow meter is used in some automobiles to measure the quantity of air going into the internal combustion engine. All modern electronically controlled diesel engines use an air flow meter, as it is the only possible means of determining the air intake for them.

The moving vane (flap) type air flow meters actually measure air volume, whereas the later "hot wire" and "hot film" air mass meters measure the mass of air flow.

The flap-type meter includes a spring which returns the internal flap to the initial position. Sometimes if the spring is tensioned too tightly, it can restrict the incoming air and it would cause the intake air speed to increase when not opened fully.