Check / replace positive crankcase ventilation control valve. Crankcase forced ventilation control valve is usually installed below the valve cover. The specific location can refer to the car manual. The general inspection is to take the crankshaft full of force forced air control valve removed from the valve cover, and then shake, if there is a click, the valve is normal. More accurate inspection steps are as follows: (1) tachometer connected to the engine. (2) With the engine idling, remove the positive crankcase ventilation control valve from its seat. (3) check tachometer readings. Press and hold the valve inlet or hose inlet with your finger and you should feel suction. (4) Check the tachometer again. At this time, the engine speed should be reduced at least 50r / min. After releasing your finger from the valve port, the engine speed should return to normal. (5) If you press and hold the valve or hose port with your finger, the engine speed does not change or the value of the change is less than 50 rpm. That is, the hose is blocked or the valve fails. First check the hose, if the hose is not blocked, replace the positive crankcase ventilation control valve.