may sound silly but think i had the same problem a while back. I had a water leak coming through my wiper arms, through the wiper motor
and through the junction box behind the steering rack and right onto my accelerator pedal. I got hacked off when i broke down on the m42 having to call the mrs to tow me off. cost me a whole £100 for a new accelerator pedal, feels worth it when i put my foot down now, i thonk its the pedal, water or not