alot of possibilites.. broken switch, bad motor, bad power lead, relay, or other wiring issue, maybe the joints of the wiper arms have to be oiled, maybe there's something restricting the chain/belt that holds them together.[addsig]
I agree about them needing oil. Mine always went slow so I lubricated everything and they work alot better
. Also could be the intermitten control module (grey box attached to lower dash by steering column.) My intermitten wipers have just done random things since I can remember and I've never bothered to fix them