The intake air pressure sensor is connected to the intake manifold by a vacuum tube. With the different speed loads of the engine, it senses the vacuum change in the intake manifold, and then converts the change of the internal resistance of the sensor is converted into a voltage signal for the ECU to correct the fuel injection amount and ignition timing angle. In the EFI engine, the intake pressure sensor is used to detect the intake air amount, which is called D-type injection system (speed density type). http://www.keditesensor.com/intake-air-pressure-sensor/