What is the reason for the oil in the accelerator? Why?

This situation is caused by the exhaust on the engine. At the position of the air cleaner, there is a pipe connected to the upper cover of the engine for discharging oil and gas. With the increase of vehicle age, the working condition of the engine becomes worse, which will discharge a lot of oil and gas and condense black oil, which will easily aggravate the pollution of the throttle. In the past, taxis took this kind of pipe to the chassis position alone and braved the faint blue smoke to prevent this.