The Mass Air Flow Sensor is a device used on many fuel injected automobile engines to measure the density of air volume entering the intake system. This, combined with other sensors, is connected to the vehicles computer to manage fuel flow and engine performance based on real-time conditions. If the sensor begins to fail, it will give you hints. According to Richard Joseph, ASE Certified Master Mechanic, the first visible sign will be the "Check Engine" light.
A Car with Hiccups
Throttle response is one of the first operational clues to a fuel system problem. A failing MAF can cause your engine to hesitate when you accelerate rapidly, stall when you apply the gas or hiccup when you change the throttle position quickly.
Another sign that your MAF is faulty is that your engine will run rough at idle or surge. The difference is a rough idle will cause vibration while sitting still and a surge will cause the engine RPMs to change noticeably without driver input.
A bad MAF may also be indicated by poor starting ability or excessive fuel use that will result in black smoke emitting from the exhaust on acceleration. A further indicator that is difficult to observe is an overly lean condition which will actually cause a slight increase in mileage but can be very harmful to the engine because it increases the temperature inside the cylinder and may lead to pre-ignition or spark knock.