The air supply system provides the supply of the amount of air necessary for the operation of the engine.
The amount of air entering the engine is determined by the throttle opening angle and the engine speed.
The air flow passes through the air filter, through the throttle body port, and into the top of the intake manifold, from where it is distributed to the engine cylinders.
When the coolant temperature is low, the idle speed control valve opens and air enters the top of the intake manifold through the bypass in addition to the air passing through the throttle. Thus, even if the throttle is fully closed, air enters the top of the intake manifold, and therefore the idle speed increases (1st stage idle speed control). The top of the intake manifold reduces airflow pulsations.