The air flow meter is simply a device used to measure the rate air is going into your car's engine. It is typically affixed to the intake manifold, and sends the data it collects to the Engine Control Unit (ECU). The ECU then regulates how much fuel should be introduced to the cylinder for optimal performance and complete combustion. If too little oxygen is available, the cylinders will have an excess of fuel, which will throw off compression and possibly cause damage to the engine's internal components. The air flow meter is especially useful when elevation varies, as oxygen is thinner higher up. The next time you're driving up and down a mountain, know your air flow meter is hard at work preventing the car's cylinders from flooding with excess fuel!