The throttle motor is part of the actuator, it's all one assembly though. In it's simplest description, it controls the throttle (the butterfly valve in the venturi). They went to this when they wanted to incorporate control of the throttle into the anti-skid control (traction control). They figured "what the heck, lets do it electronically all the way, then we can use it for idle control and cruise control too". My experience on bad ones has been mostly with the 119 motor V8, the 104 motor I can't recall replacing one personally. I think the heat gets to them on the 119 motor, it has to get hot practically buried in the valley between the heads. Usually they are going into a back-up mode called "limp home mode", either that or they idle bad like yours is.
I still maintain that since it works OK off idle, not in limp-home mode, and that the air mass meter was replaced, that the tech may have reset the self-adaptation of the fuel trim and neglected to reset the throttle stop position. I believe that on these, you erase the throttle valve stop (electronically) when you reset the self-adaptation. Maybe the tech is unfamiliar with this procedure and started learning the throttle stop, thought it was done and removed his scanner early? Given the scenario, I would "back up" and look things over more closely, at least try having the throttle stop relearned before going this route. Just to much "coincidence" for me to start ordering parts already.