Q: How much can the fuel consumption of a car with 2.0 displacement be reduced after cleaning the throttle and changing the oil every time compared with that without changing it?

Cleaning the throttle body will not save fuel, but will consume fuel at idle speed, which will only reduce the wear of the throttle body caused by carbon deposition and improve idle speed. You will save fuel at the beginning after oil change, because the friction resistance is small just after oil change, so you will save fuel. Fuel saving is related to road conditions, vehicle speed and oil change level, so it is uncertain.