Air Management: Notes
Throttle Valve: The mechanical throttle valve regulates the intake air flow and it is linked by a cable to the accelerator pedal.
The throttle housing is secured to the intake manifold by four bolts (arrows).
The throttle valve is heated by engine coolant to prevent condensation from "icing". The throttle valve is "preset" and should not be adjusted.
Throttle Position Sensor: A potentiometer is mounted on the throttle housing which provides the ECM with a voltage value (0-5v) that represents throttle angle position and rate of movement. The sensor receives its power supply from the ECM.
The Potentiometer is non-adjustable because the ECM "learns" the throttle angle voltage at idle speed. If the throttle position sensor is replaced, the adaptations must be cleared using the DIS/MoDIC.
If this input is defective, a fault code will be stored and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will still operate the engine using the Hot-Film Air Mass Meter and Engine RPM inputs.
Idle Speed Control Valve: This valve regulates air bypassing the throttle valve to control the engine idle speed.
The valve is supplied with battery voltage from the ECM Relay. The Idle Air Actuator is a two-coil rotary actuator. The ECM is equipped with two final stage transistors which will alternate positioning of the actuator.
The final stages are "pulsed" simultaneously by the ECM which provides ground paths for the actuator. The duty cycle of each circuit is varied to achieve the required idle RPM.
If this component/circuits are defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved.
Hot-Film Air Mass Meter (HFM): The air volume input signal is produced electronically by the HFM which uses a heated metal film (180°C above intake air temperature) in the air flow stream.
The ECM Relay provides the operating voltage. As air flows through the HFM, the film is cooled changing the resistance which affects current flow through the circuit. The sensor produces a 1-5 volt varying signal. Based on this change the ECM monitors and regulates the amount of fuel injected.
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will operate the engine using the Throttle Position and Engine RPM inputs.
Air Temperature Signal: This signal is needed by the ECM to correct the air volume input for changes in the intake air temperature. The sensor is located in the intake manifold behind the throttle housing.
The ECM provides the power supply to this component. The sensor decreases in resistance as the temperature rises and vice versa (NTC). The ECM monitors the applied voltage (5v), as air temperature changes the resistance value the voltage signal will vary (0-5v).
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will operate the engine using the Engine Coolant Sensor input.
Pressure Control Valve: The pressure control valve varies the vacuum applied to the crankcase ventilation depending on engine load. The valve is balanced between spring pressure and the amount of manifold vacuum.
The oil vapors exit the separator labyrinth (2) in the cylinder head cover (1). The oil vapors are drawn into the cyclone type liquid/vapor separator (3) regulated by the pressure control valve (5). The collected oil will drain back into the oil pan (4).
At idle when the intake manifold vacuum is high, the vacuum reduces the valve opening allowing a small amount of crankcase vapors to be drawn into the intake manifold. At part to full load conditions when intake manifold vacuum is lower, the spring opens the valve and additional crankcase vapors are drawn into the intake manifold.
- Engine Oil Vapors
- Collective Drain Back Oil
- Oil Vapors to the Intake Manifold