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As I understand Bosch fuel injection, the system elicits inputs about the outside world, does math and then sends out instructions to the various components within its control.
One of the inputs of interest is whether or not the driver’s foot is on or off the throttle. These two modes clearly signify a different intent. For that reason, one basic function of the throttle position sensor is to sense which one of the two modes applies.
Another input of interest is whether or not the driver’s foot is pressing the accelerator pedal all the way down. These two modes also signify a very different intent. For that reason, another basic function of the throttle position sensor is to sense which one of the two modes applies.
I own an old BMW 745i and it behaves very differently when the accelerator pedal is all the way down vs. not. Presumably back in 1984 when the car was working correctly, it went way faster with the accelerator pedal all the way down. Nowadays, it stalls. The difference is like night vs. day. I’m guessing that as soon as the throttle position sensor senses that the car is at wide open throttle, it sends a signal to the fuel injection computer, which goes into a special mode, which malfunctions.
As I recall, at wide open throttle, some of the emissions limits are lower, so the fuel injection computer optimizes for maximum power with less of a focus on fuel economy or emissions.
Hypothetically, it might also be of interest to the fuel injection computer at which position the throttle is, even if not fully open or fully closed. However, with the possible mechanical variances in throttle position, I can see how this might be subject to some imprecision, which is probably why the system relies instead on actually measuring how much air is flowing into the intake system.
From what I’ve read, some BMWs do have a rheostat built into the throttle position sensor, but the 318i doesn’t. So, the functions of this part are in some ways a lot more simple:
- Throttle completely closed, or not
- Throttle completely open, or not