An air flow meter varies its signal by the deflection of a vane as air enters the engine. Deflecting the vane moves contacts across a potentiometer, to signal its position, and thus, the amount of air entering the system.
The temperature sensor uses material with a negative temperature coefficient of resistance. Its resistance is high when it’s cold, but it falls as its temperature rises. It is called a thermistor. This is the opposite of a normal resistor, which increases its resistance as temperature rises.
The coolant temperature sensor is immersed in coolant , in the cylinder head.
The air temperature sensor is in the air intake - at the airflow meter, or in the manifold.
Throttle position can be signalled by a potentiometer attached to the throttle shaft. It provides a continuous, varying signal, through the entire range of throttle position. Throttle position can also be signalled by a contact-type switch, but it signals the idle and fully open positions only.
Engine speed can be detected by a connection from the ignition system primary circuit, or by a pulse generator-type sensor, on the crankshaft. The pulses are computed by the control unit , into an engine RPM figure. They can also be used to trigger the injectors.
