An intake manifold air leak is characterized by lower than normal manifold vacuum. Also, one or more cylinders may not be functioning. USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR THE FAN. DO NOT WEAR LOOSE CLOTHING.Start the engine.Spray a small stream of water (Spray Bottle) at the suspected leak area.If engine RPM'S change, the area of the suspected leak has been found.Repair as required.