as you say, there should be 2 ways to adjust the throttle.

the first is to set the plate angle at rest with a screw, and then there is a tapered bypass screw to let air past the throttle plate. these should be set with the ngine up to running temperature, but no electrical load on it (fans not running etc) and the ISCV unplugged

then of course, the Idle Speed Control Valve should do it's stuff when the engine is cold and when loaded