The speed adjustment knob is simply an air bypass. Its in and out ports are in parallel with the IAC. The unsteady and high idle, would suggest the throttle is not closing all the way (probably linkage adjustment) and preventing the TPS idle switch from closing. You should hear a distinct "click" at the TB as you get to or come off of idle position.

You are unclear about whether your failure was after all those parts were replaced, and whether the failure was at idle or under load. If it fails again, post ALL the numbers for gasses, including the limits for each mode.