Why are there no maintenance items such as "cleaning the accelerator and carbon deposition" in the car maintenance manual?

Yes, because it is in deep maintenance and it is not mandatory to replace it. Generally, old cars have to clean the throttle, or the road conditions are poor and there is a lot of dust. Under normal circumstances, frequent air filtration can be avoided. There is also cleaning the oil circuit. The internal cleaning and protection of the engine are carried out according to the wishes of the owner. It is certainly beneficial to do it, and it is ok not to do it. In fact, the maintenance of cars still depends on the usual care of car owners. It is best to change the oil one or two hundred kilometers in advance. You must heat the car in winter. How good you are to the car, the car will be!