if your IAC is too slow, throttle follower doesn't fix it or settings not available, and you want your idle to drop quickly, you can play with your timing advance vs idle error settings or whatever it's called in your definition. actually that's a very powerful setting that can increase or decrease cam lope and other things. another way to roll is you can close off the IAC passage by an aribtrary amount and then muck with your throttle plate. that way the IAC only makes fine adjustments and the throttle plate does its thing. finally on race cars i have deleted the IAC and just set a slightly higher idle that runs a bit crappy for the first few seconds but cleans up real quick as startup enrichment tapers off.