Why is there a small amount of oil at the throttle of Passat?

This is normal. Because the oil in the engine will produce steam after heating, most carburetor cars in the past are directly discharged into the atmosphere. But it will pollute the atmosphere.

All EFI vehicles have a pipeline to guide the oil vapor to the intake pipe, and then enter the cylinder for combustion. The oil in the throttle valve is the residue of oil vapor.