Throttle adjustment, general
The throttle is turned by a DC motor via a reduction gear. ECM supplies the motor a PWM signal from pins 15 (A) and 31(A). ECM can turn the throttle disc in either direction, i.e. in a closing or opening direction. A spring strives to keep the throttle in a slightly open position, which is its rest position.
Scheme 630
During limp-home in the throttle control, it is this position that provides the throttle area and thereby controls the air mass/combustion that can enter the engine. Cylinder cut-off (fuel cut-off) and ignition timing are used as regulating instruments to control engine torque. Idling speed is about 900 rpm. The engine runs unevenly at low load due to cylinder cut-off. The car can be driven, but with greatly reduced performance.
Two throttle position sensors are connected to the shaft. The sensors comprise potentiometers that are supplied 5 V from ECM pin 54(A) and are grounded in ECM pin 39(A).
The voltage from potentiometer 1 is connected to ECM pin 55(A) and increases as the throttle opening (area) increases. Voltage from potentiometer 2 is connected to ECM pin 8(A) and reduces as the throttle opening (area) increases. Thus, the total of the voltages is always 5 V.
Scheme 631
ECM uses the value from potentiometer 1 to detect the current throttle opening (area).
Turbo adjustment
The airflow from the turbocharger is regulated by a solenoid valve, which controls the exhaust turbine wastegate pneumatically.
Scheme 632
The solenoid valve (179a) is supplied voltage from the main relay (229) and is grounded from control module pin 14(A) with a 32 HZ PWM. The wastegate valve goes opposite the closing direction when the pulse ratio increases, thus increasing compressor flow.
When the requested air mass/combustion (torque) is too great to be regulated by the throttle alone, the turbo control must satisfy the excess requirement. The excess is converted to a PWM that controls the charge air control valve.
ECM calculates the necessary (requested) boost pressure to achieve the desired engine torque.
The values for atmospheric absolute air pressure and intake air temperature are used to correct the conversion. At low atmospheric pressure or when the intake air temperature is high, a greater PWM ratio is required to obtain the same engine torque.
Scheme 633
The control module checks that the actual boost pressure agrees with the requested one. If necessary, the PWM ratio is fine-tuned by being multiplied by a correction factor.
The correction factor (adaptation) is stored in the control module memory and is always included in the calculation of the PWM ratio.
The purpose is to make actual torque and request torque the same as soon after a load change as possible.