Throttle Body: Description and Operation

THROTTLE BODY WITH TAC AND INTEGRAL THROTTLE POSITION SENSORS

Throttle Body With Throttle Actuator Control (TAC) And Integral Throttle Position Sensors:

The L61 engine does not use a traditional throttle control cable to control engine speed. The L61 engine uses a throttle body with Throttle Actuator Control (TAC) to control air flow to the engine. The throttle body contains a direct current stepper motor that is controlled by the ECM. The ECM is able to control the stepper motor by moving the throttle plate in either direction to increase or decrease air flow to the engine.

No Idle Air Control (IAC) valve is used to control idle speed. The ECM controls idle speed by commanding the throttle plate open.

The Throttle Position (TP) sensors are mounted on the throttle body and cannot be serviced separately. The sensors are potentiometers with independent 5 volt supply, ground and signal circuits. As the throttle opens, the signal wire on sensor 1 decreases from a value near 5 volts toward zero volts. The voltage on the signal wire for sensor 2 increases from a value near zero volts at idle to a voltage near 5 volts at WOT. The two potentiometers are redundant to one another, each using the other as a backup should of the potentiometers fail.