If you are saying the stick in the transmitter itself is springing back then the airplane and it's radios/linkages can have nothing to do with it. (assuming it isn't laying on the transmitter
)
There should be no springs involved with the throttle gimbal in the transmitter but it is possible something broke off or fell in there and is binding the gimbal (stick). Do all of the others controls function correctly? If not a piece of one of them may have popped loose and fallen into the mess. Give the unit a careful inspection to look for something that doesn't belong there and maybe turn it upside down and shake gently while moving this stick carefully. You may get lucky and have it fall out.