I haven't experienced your exact problem , but I have had erratic wiper movement. My wipers stopped completely and I changed the modulator box, after that all I could get to work was one speed, low, no intermittent, no high. I figured I must have messed up the wiring somehow. I'm not very good at electrical problem solving and haven't had a chance to take it in to have it looked at, that was months ago. then just last week when I tried them everything worked, which leads me to believe that the wiper arm assembly may possibly have a short in it somewhere.