How have you confirmed that it is a problem with the throttle body or cable and not something else?

Check the cable and throttle body. Remove the cover off the top of the throttle wheel by removing the one Torx screw (the one in your toolkit will do). With the car cold and not running, turn the wheel/cam observing the action of the cable and linkage to the throttle body. Remove the throttle cable and repeat. The wheel and linkage should move freely against the resistance of the spring and should spring back shut. With the cable free, check the action of the accelerator pedal. That should isolate whether the problem is in the cable or the linkage/throttle body. If it's the cable, I'd suspect some moisture (frozen) or greasiness in the sheath. Working some WD-40 down it might help.

WARNING: A stiff throttle has potential to be a very dangerous thing if it were to become stuck open. (That's why I'm skeptical that the problem lies in that area - Carmakers are careful to make the setup work in all conditions) Also, when putting the throttle cable back on the wheel/cam, be careful to get the cable properly seated back in the correct slot. Work it a few times to be sure.

-Will