Double check the fast idle screw isnt too tight.
Loosen screws on throttle blades and recenter them in the bores.
A faulty APT adjustment could keep the primary rods from fully seating in the jet, richening the mixture. Easy enough to check though with the air horn off. Idle mixture screws on a Q jet really dont adjust the A/F mixture, they simply adjust the volume of the available mixture below the throttle plates.