Throttle Body: Description and Operation

Upper Manifold Assembly Air Flow Diagram:

The upper manifold assembly is a single casting that includes the intake plenum and the throttle body. The throttle valve is used to control air flow into the engine, thereby controlling engine output. The valve is opened by the driver through the accelerator controls. During engine idle, the throttle valve is almost closed, and air flow control is handled by the Idle Air Control (IAC) valve.