Wow that is strange... maybe a bad motor or a gear that is striped? on my old truck (cheebe) the switch was bad and you would turn on the wipers and they would go, then when you turn them off, they would keep going. you typically had to turn the switch on/off a few times to get them to turn off. once in a while you would turn them on and nothing would happen, then you needed to turn the switch a few times to get them to come on.