I have a '08 F350 with the 6.4 in it and lately after I wash it or drive in the rain, the wrench light comes on the instrument cluster. When this happens, I loose throttle, I can push the accelerator and it does nothing. When I let off it will idle up by itself and when I tap the break it idles back down. Any suggestions? I think it could be the TPS sensor but I am not sure and if so does anyone know where it is located on the truck?