99 Tacoma Wiper Motor Problem

While driving in heavy sleet and snow recently, my wipers suddenly stopped in the down position. Upon closer inspection, I found they had actually gone down past the windshield and are resting on the plastic vented piece between the hood and windshield. With the wipers turned on, I can manually move them back and forth quite easily, but they do not move by themselves. After a couple of minutes, it's like the motor finally kicks in, and abruptly lowers the wipers back down past the windshield. Thawing the truck out completely and cleaning all ice from the area has had no effect. Any help would be appreciated.