Throttle Body: Description and Operation

Throttle Body Assembly:

Throttle Body Assembly - Exploded View:

DESCRIPTION
The throttle body assembly is attached to the intake manifold plenum, and is used to control air flow into the engine, thereby controlling engine output. The staged throttle valves within the throttle body are opened by the driver through the accelerator controls. The small 22 mm (0.87") primary throttle valve provides smooth low speed operation, while the large 59 mm (2.32") secondary valves provide high volume air flow for maximum engine power.

OPERATION
The primary throttle valve is operational when the vehicle speeds are less than approximately 113 km/h (70 mph) (level terrain cruise). The secondary throttle valves are opened at approximately 80° of primary throttle opening. During engine idle, the primary throttle valve is almost closed, and air flow control is handled by the Idle Air Control (IAC) valve. To prevent throttle valve icing during cool weather operation, engine coolant is directed through the coolant cavity in the top portion of the throttle body.

Vacuum ports are located at, above, or below the primary throttle valve to generate the vacuum signals needed by various components. The throttle body also provides the location for mounting the Throttle Position Sensor (TPS).