Many times a "sticky" passage set like yours can be caused by slight mis-alignment of the knob parts with the internal mechanism. Things shift over time (mostly droop, but that's a personal problem).
So pop of the cover plate, there's a slot you stick a flat bladed screwdriver into (I think I see it at 2 o'clock), unscrew the knob and remove it. Then lube up the mechanism from the inside as well as along the bolt on the outside. Reassemble and screw down the 2 screw LOOSELY and try it, jiggle the knob if needed. It should operate freely. Snug the screws down a bit more, but not tight yet, try operating the knob again and if still running wild and free, tighten the screws fully and tap the cover plate back over the mounting plate. (You did remember to put the cover plate on before reassembling, RIGHT?!) It should operate much better now, if not, time for a trip to the hardware store.
OH and an LOL shout out to Freeman for a great comment, I thought the same thing!!!