Make sure you're not exposing too much of the 'idle transfer slot' at idle (primary throttle blade adjustment). Common problem. If so, you'll need to open the secondary blades a little bit, in order to close the primary blades (without altering the idle speed). Holley has a good video pertaining to this: http://www.youtube.com/playlist?list=PL353239D6A7D7BFF0 (Click "How To Adjust The Secondary Speed Screw") View all their carb tuning videos!
May God's grace bless you in the Lord Jesus Christ.
'78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, cold air induction, dual 3" exhaust/Magnaflow mufflers, 100HP progressive dry direct-port NOS, A/C, Lentech Strip Terminator wide-ratio AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, custom traction bars, 4" lift, 35" mud tires