When going downhill, the low-speed braking engine is higher, so is the throttle valve wider? Is it beneficial to remove carbon deposits?

Let me tell you without hesitation that a high engine speed does not necessarily mean that the throttle is on. For example, in your current situation, the accelerator will not open when the engine speed is high, unless you are still stepping on the accelerator when going downhill. This is because the engine speed is getting higher and higher due to the acceleration of gravity. Because the accelerator is not on, the fuel will not increase with the increase of vehicle speed. On the contrary, fuel injection is sometimes stopped by computer control. Because stopping oil injection or spraying a small amount of oil can't produce a high airflow, so the carbon deposit can't be discharged! To sum up, the throttle valve of 1 cannot be opened, and the carbon deposit cannot be discharged.