Air Intake System

Air Intake System

Air Intake System Components:

The air intake system delivers filtered and controlled airflow to the engine. Three groups of components make up the system: air handling, sensors, and control devices.


Air Intake System Air Handling Components


Air intake system air handling components include the inlet air duct, air cleaner, throttle body, intake manifold, and three resonance chambers or resonance ducts. The resonance chambers suppress air inlet noise caused by airflow pulsations. The throttle body contains the throttle valve and throttle position sensor. The Idle Air Control (lAC) valve also mounts to the throttle body.


Air Intake System Sensors


Air intake system sensors include a heated resistor-type Mass Air Flow (MAF) sensor and Throttle Position (TP) sensor, both supply data to the PCM. The PCM also monitors engine speed.


Air Intake System Control Devices


The Idle Air Control (IAC) valve helps to maintain a steady idle speed when heavy mechanical or electrical loads are added to the engine. The PCM responds to changes in the engine idle speed due to changes in the engine load condition by regulating the idle air control solenoid valve. The IAC valve is combined with the Fast Idle Control (FIC) solenoid. The AC valve must be replaced as an assembly with the FIC solenoid.


Bypass Air (BPA) Control Systems


The BPA control system maintains engine idle speed quality throughout the engine's operating modes by means of the IAC valve.


The BPA valve provides bypass air to the intake manifold when the engine is cold, for a fast idle during warm-up. The BPA valve is controlled by the PCM (through the Fuel Pump Relay) at the same time as the Fuel Pump Control.


The BPA valve responds to changes in the engine coolant temperature only. As the engine warms up, the bimetal moves, pushing the valve closed and reducing the bypass airflow amount. The bypass airflow is at its highest level during cold engine start. It declines steadily until reaching a coolant temperature of 80°C (176°F), at which time the flow is completely cut off.