Intake manifold swirl valves

why is there a problem ? an intake has contours to evenly and efficiently get air and fuel into the cylinder , never heard of swirl valves

Swirl or butterfly flaps are located inside some intake manifolds to control the airflow. There could be a problem when they or the metal rod that holds them gets worn. They can chatter and create a knocking sound. If they break off and end enter the cylinders, they can destroy an engine. I have a knocking sound in mine. Don't know if Ford put swirl flaps in this make and model's intake manifold.