+1 on the PCV cover.
Remove the spark plug cover and find the round disc with a vent at the top right. Stick your finger over it - if working properly, you should NOT feel suction or be able to discern a change in idle.
Remove the spark plug cover and find the round disc with a vent at the top right. Stick your finger over it - if working properly, you should NOT feel suction or be able to discern a change in idle.