More specifically, what additional parts/sensors/systems are active/activated when the car accelerates vs when you revving the engine in park? How does the electrical system differ between the two? If you can go into depth with using a 2000 Civic (or any other 6th gen Honda) then that'll be even better.
There aren't any additional sensors that are activated or inactivated when you are in Park or Drive. The ECU will manage the engine the best in can at all times based on sensor inputs.
Basically, revving the engine is the result, not the cause. When you hit the accelerator, the throttle plate opens, the engine suck more air in, the ECU sees that and adds more fuel. Park or Drive will just determine what the transmission will be doing with all that spinning transmission fluid. Park or Drive only changes the mechanical configuration of the transmission.
manual transmission neutral
- the computer will be monitoring a high vacuum normal rpm state using little fuel and air.
- this may trigger some checks in the drive cycle that are rarely done
- the radiator fan may turn on due to lack of air flow
manual transmission 1st gear
- the computer will be monitoring a high vacuum normal rpm state with more airflow and fuel
- the speedometer will be moving
- the odometer will be moving
- abs systems and traction control systems will start picking up tire rotation info
automatic trans in neutral
- nearly the same as the manual trans in neutral
auto trans in drive
- nearly the same as a manual in drive but with added transmission functions
- the transmission will be monitoring internal pressures that tell it when to shift and lockup the torque converter
from car to car and with more sophisticated computers more monitoring will happen while in all these states. Older vehicles will have less stuff happen.