a method of determining an engine intake air leak may include measuring an air flow rate into an internal combustion engine , comparing the measured air flow rate to a first predetermined air flow limit , calculating an estimated air flow rate into the engine when the measured air flow rate is less than the first predetermined air flow limit , comparing the estimated air flow rate to second and third predetermined air flow limits , and indicating an air leak when the estimated air flow rate is greater than the second predetermined air flow limit and less than the third predetermined air flow limit .