The throttle lever just has a small plastic spring lever for return action.
So if it gets dry or some sand in it could stop it working.
You could try to spray some lube in from the side to free it not to much.
See how you go 2nd option is to take off the plastic panel and lube the plastic spring.
I had the same issue after the dealer replaced my steering. They caused it by improperly removing the throttle sensor. I had the column replaced twice, before the recall came out and with the recall. They messed it up both times. They also screwed up the IBR sensor the second time. When the sensors are removed improperly the spring wrapped around the sensor pops out of its hole. It's a little tricky, but you can just pop them back together. It was easier than driving back to the dealer.