Intake Air Plenum: Description and Operation

Intake Manifold:

DESCRIPTION
The intake manifold is made up of the upper and lower manifold assemblies.

Upper Manifold
The upper manifold assembly (1) is a single casting that includes the upper portion of the air chamber (plenum) and the air inlet (fitted with a throttle valve). This assembly replaces the individual throttle body assembly and plenum components. The throttle valve is used to control air flow into the engine, thereby controlling engine output. The throttle valve is opened 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)(2) valve. Vacuum ports located at, above, or below the throttle valve generate vacuum signals needed by various components. The nonadjustable, throttle shaft-driven, Throttle Position (TP) sensor (3) is attached to the upper manifold assembly opposite the throttle cam lever.

Lower Manifold
The lower manifold (5) is a single casting that includes the intake runners and a longitudinal fuel passage (6) with intersecting fuel injector bores in each runner. This assembly replaces the individual fuel rail and manifold components used in other systems. Information on the fuel injectors (7) and pressure regulator (4) are covered separately.