If the idle control valve is going to atmosphere do you have the charge carrier vlaneked or are you still using the escort one? Also wouldnt you lose some boost through the idle control valve runing to atmosphere or does it completely shut off when not being used. With regards to idle like safe chav says its predetermined by the ecu you can set base idle with iscv disconnected and adjust the screw you mention should be around 600rpm i think. Is the valve operating properly and not all gummed up?