There's a rotating vane valve in the ICV. When the ICV is unpowered, it rotates to a fixed opening point. So it still flows air, it just doesn't control the flow. When you power it up it actually rotates to close that baseline opening and opens a gap on the other side of the valve.
The throttle plate isn't supposed to be completely closed. There's a calibration to set the correct air flow at idle, but it requires Alfa flow tools that you don't have. Since it's been messed with anyway, maybe try *opening* it a bit more using the adjustment screw? It sounds like you're not getting enough air at idle, and if the throttle plate is too closed that might be part of the problem.
I tried this before but I didn't change the TPS because the idle was quite high so I thought it's pointless.
However, it sounds like the ICV might actually be less open when connected than when disconnected - that's what I didn't account for.
I'll try increasing it by about 100-200 RPM and then adjusting the TPS so it knows it's at idle,
and if the ICV is less open that might actually drop the high idle.
But what I don't understand is - why is it Ok with the current settings when warm and not ok when cold.
Is the O2 sensor active immediately or only after it warms up?