A method of modifying an air intake manifold to control air intake runners. The method includes the steps of providing a cartridge including a plurality of compartments, each spaced apart to define a groove therebetween, snap-fitting a bushing carrier having a rotatable bushing into each of the grooves, positioning a flap having a slot over each of the compartments, inserting a shaft through each slot and each bushing thereby rotatably retaining each of the flaps within one of the plurality of compartments, positioning the cartridge over the air intake manifold so that each of the plurality of compartments is substantially axially aligned with one of the air intake runners, and removably connecting the cartridge with the air intake manifold.