Air Induction System

GENERAL
Air which is drawn in and filtered by the air cleaner is metered and sent to the throttle body via the air intake boot. From the throttle body, the air is regulated by the open-close operation of the throttle valve and is delivered to the intake manifold. It is then distributed to the respective cylinders to mix with fuel injected by the fuel injectors. Thus, the air-fuel mixture is delivered into the cylinder. Part of the air branched at the upstream of the throttle body is sent to the idle air control solenoid valve which regulates engine idle speed.


MASS AIR FLOW SENSOR




- The MFI system employs a hot-film type mass air flow sensor
This mass air flow sensor converts the amount of air taken into the engine into an electric signal by utilizing the heat transfer phenomenon between the incoming air and a heating resistor (hot film) located in the air intake.
- The features of this flow sensor type are as follows:
1) High-altitude compensation is made automatically.
2) Quick response.
3) These are no moving parts.
4) They are compact.


THROTTLE BODY
- In response to the depressing stroke of the throttle pedal, the throttle body opens/closes its valve to regulate the air volume to be taken in the combustion chamber.
- During idling, the throttle valve is almost fully closed and the air flow through the throttle body is less than that passing through the carburetor.
- More than half of the air necessary for idling is supplied to the intake manifold via the idle air control solenoid valve.
- And the idle air control solenoid valve properly controls the engine idle speed, so it does not need to be adjusted.


THROTTLE POSITION SENSOR




- A throttle position sensor is provided with a potentiometer which is interlocked with the throttle valve shaft.
- This throttle position sensor sends the ECM a potentiometer output signal corresponding to the opening of the throttle valve. When the level of this signal exceeds a predetermined value, the ECM interprets it as complete closure of the throttle valve and makes a control most suitable for the engine operation with the throttle valve fully closed. For correcting error of this signal, the ECM is provided with a learning function.
- Thus, the ECM precisely controls the air-fuel ratio during acceleration and deceleration as well as engine idling.


IDLE AIR CONTROL SOLENOID VALVE




- Idle air control solenoid valve consists of an air cut valve, duty control valve, intake air passage and a coolant passage.
- Air cut valve contains a bimetallic substance which responds to coolant temperature, and a duty control valve which is operated by a signal sent from ECM.
- When engine coolant temperature is low, air cut valve is fully opened by the action of the bimetallic substance so that the air flow required for low engine coolant temperatures is maintained.
- ECM controls duty control valve to bring the operating engine speed as close to preset idle speed as possible.