OK, have removed the ICV again. The resin plug hides the brass head of what looks like a small grubscrew with a wide flat base inside the ICV. The base seems to limit the rotation (around a vertical axis) of the internal rotary valve of the ICV, so theoretically could be made to vary the idle speed. The head is hollow, shaped for approx 2mm Allan key, and the exterior is also hex, about 4mm dia. Have carefully drilled out the resin with a 1mm drill. But, it is too tight to turn with Allan key or pliers or both (both is best as otherwise it cracks). I cannot see any thread on it, so don't know if it can be turned - it may be a pressfit. Does anyone know? If not, I may have to drill it right out, re-thread and insert a substitute adjustment screw. Any other suggestions?