Although it could be any of these things, the throttle position sensor is more likely the culprit. It gets worn out right where the throttle starts to move, since that is where it is most of the time. They don't cost that much (35$-55$) and they are easy to install yourself. You can test it with a meter, but it's the only sensor that physically moves, so it's not a question of if it will die but when.
