Most likely the fast idle cam is contacting the fast idle screw and hanging the primary throttle blades open. Examine the choke area very closely and you will likely see the problem.
With the choke wide open the fast idle cam should allow the blades to fully close when you open the throttle some, then allow it to close again. When the fast idle is disengaged, the curb idle screw will contact the linkage as it should. Once that's taken care of, the idle mixture screws will become responsive.