you say you have fitted a new idle valve, check you have the correct one, as there are to types which look exactly the same, check the top of the valve there should be a stamp on the top, if your new valve has a different number than the old valve try swaping the wires around in the isv loom plug and see if it makes any differance, had the same problem on 2wd sapp, turned out that the new valve was for escos swaped wires around and was fine.