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 valve is a two stage (progressive linkage) plate arrangement with integral closing springs. This allows a smaller primary opening for low to mid-range RPM and a larger secondary opening that opens for the higher RPM range.

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 ECM must be disconnected from the power supply for at least one minute (to clear memory).

Idle Speed Control Valve:  This is a two wire control valve that regulates air by-passing the throttle valve to control the engine idle speed.

The idle speed control valve is spring loaded closed. It will "failsafe" to a fixed opening (21%) to allow the engine to idle in the event of a power failure.

The valve is supplied with battery voltage from the Engine Control Module Relay. The valve opening is controlled by the ECM modulating the ground signal which opens the valve against spring tension.

Air Flow Volume Sensor:  This sensor measures the total volume of air drawn into the engine.

The ECM provides the power supply for the Air Flow Volume Sensor. A potentiometer is connected to the sensing flap and as air flow causes the sensing flap to move, a varying voltage signal (0-5v) is sent to the ECM that "represents" the inducted air volume.

Attached to the sensing flap is a "compensation flap" that moves within a closed chamber. This creates a dampening effect on flap movement for pulsations in the intake system caused by cylinder filling and intake valve operation.

Air Temperature Signal:  The Air Flow Volume Sensor contains an integral air temperature sensor. This signal is needed by the ECM to correct the air volume input for changes in the intake air temperature (air density).

The sensor is located in front of the measuring flap. 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 an applied voltage to the sensor (5v) that will vary as air temperature changes the resistance value (0-5v).

Differential Air Intake System (DISA):  DISA allows the dynamics of varied intake manifold tuning. This feature provides necessary intake air "velocity" producing good mid-range torque. Additionally, DISA can divert intake air flow providing "volume" for higher RPM requirements.

The ECM closes the changeover valve to take advantage of a long single intake runner at midrange RPM. This produces air velocity  that increases engine torque at mid-range.

At high RPM, the ECM opens the changeover valve allowing the engine breathing dynamics to change to the dual short air pipes (volume)  . This change enables additional power output at the higher RPM range.

To accomplish this function, the M42 intake manifold incorporates a non-replaceable brass change over valve.

The DISA system vacuum components are:

• Motor (actuator) 
• Reservoir 
• Solenoid 
• Check Valve 

The solenoid receives voltage from the Engine Control Module Relay and the ECM controls the ground supply to activate the solenoid.

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 in the cylinder head cover (1). The oil vapors are drawn into the intake manifold (3) regulated by the pressure control valve (2).

At idle when the intake manifold vacuum is high, the vacuum decrease the valve opening and only allows 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.