The throttle blade set screw is not the problem. By unplugging the IAC from the harness you are elminating the ECU control for idle and relying soley on the TB blade position. The car would do exaclty what yours did when you removed the IAC from the harness, idle down to the point of almost stalling. That means the TB blade position is correct. I wouldn't play with the TB blade set screw. It will not alter the idle.