This sensor gathers information on throttle positions, to allow the control unit to make adjustments according to operating conditions. It is located on the throttle body, and operated by rotation of the throttle spindle or shaft. Throttle position is sensed by a contact type switch, or a potentiometer. The switch type has 2 contacts - idle and full load. It can be supplied with a voltage to the centre terminal of its connector.
At idling speeds, the full load contacts are open. The idle contacts are closed and the signal to the computer provides for a mixture to maintain idle quality, and stability. Slightly rotating the throttle shaft opens the idle contacts. As the throttle approaches the wide-open position, the full load contacts close. The ECU reads the full-load signal, and enriches the mixture to suit.
The “idle contacts closed” signal can also be used, with the engine RPM signal to the control unit, to stop fuel delivery on engine over-run. This can be done, for example, if engine speed is above 2500 RPM on deceleration. If the ECU reads a figure above this, and also receives a throttle closed signal, it opens the injector electrical circuit, and stops fuel delivery. As RPM falls below, say, 2100 RPM, the circuit is restored. Injection then recommences, to maintain drive ability.
A potentiometer-type sensor monitors throttle position over its full range. One end has a 5 volt reference voltage from the control unit. The other is connected to control unit earth. A third wire runs from a sliding contact in the throttle position sensor, to the input circuits of the control unit. The sensor then works like a variable resistor. As the angle of the throttle valve changes, so does the voltage signal along the third wire.
At closed throttle, the reading is usually below 1.25 volts. As the throttle valve opens, the voltage signal rises. At wide-open throttle, it’s about 4.5 volts. This ongoing monitoring of throttle position provides more data for the control unit. This allows control over a wider range of operating conditions.
Source: CDX Global
