What causes the air leakage of valve cover?

Air leakage from the valve cover will make the vehicle unable to drive. When the mixture is too rich or too lean, the fuel in the combustion chamber is not completely burned, resulting in an increase in fuel consumption. It will also cause the car to accelerate slowly. The engine is difficult to start, the power is reduced, the combustion is incomplete, and the carbon deposition is serious, which may even lead to the failure of individual cylinders. Generally speaking, if there is oil leakage, it is recommended to replace the valve cover.