Throttle control, principle
The value from torque control is converted to air mass/combustion. Throttle control converts this to a specific requested value for throttle position sensor 1 and compares the requested value with the actual sensor value. The difference (deviation) gives rise to a throttle motor PWM of a magnitude and polarity that will turn the throttle until the desired value (area) is obtained. If there is a major fault in throttle control, it is deactivated and the throttle disc assumes its rest position, which is controlled by a spring. At this time, engine torque can only be regulated through cylinder (fuel) cut-off and ignition timing.
When the system's total requested air mass/combustion (engine torque) has bee calculated it is realized by the throttle and, if necessary (high engine load) turbo control. CVCP control works in parallel with the throttle and turbo control.
Requested air mass/combustion is corrected with the density of the charge air (air before throttle). Thinner air (lower density) gives a greater throttle opening angle (larger area) so that the same air mass/combustion is obtained as with normal air density.
Air density is calculated using the charge air absolute pressure and the temperature.
This value is converted to a certain requested value for throttle position sensor 1. The requested value is compared to the current value of the sensor. The difference (deviation) gives rise to a throttle motor PWM of a magnitude and polarity that will turn the throttle until the desired value (area) is obtained.
The PWM value is finely adjusted if necessary so that the requested position agrees with the current one, i.e. zero deviation.
If the requested air mass/combustion is too high to be treated (attained) by throttle control only, the excess (difference) is handled by turbo control.
In the event of a safety-related fault in throttle control, it will go into limp-home mode. The Check Engine symbol will illuminate immediately. A message appears in SID to indicate that engine performance is limited.
Note. It is entirely normal if the throttle is not completely open when the accelerator pedal is completely depressed.