The air sensor in the intake manifold, also referred to as the MAP sensor, measures the absolute pressure in the engine's intake system. It is fitted directly in the manifold or connected to it by means of a special tube. Its malfunction is usually caused by the contamination of the connecting tube or a short circuit inside the sensor. The following symptoms might indicate that the sensor has failed: improper operation of the engine, jerking, the "check engine" light is on, idle speed fluctuation.