I was recently driving in rain at approximately 70mph in my 2005 Seat Altea Reference 5-door 1.6 petrol with the windscreen wipers on full speed. When the wipers were moving in the direction of travel of the car, i.e against the wind, the car would slow down/lose some power. When the wipers moved in the opposite direction there was no loss of power. It was as if the wind screen wipers took power away from the engine when they worked hardest.

This problem is only experienced when travelling at around 70mph in fifth with the wipers on full speed. Do you know what this problem could be? I have contacted a Volkswagen and a SEAT workshop and asked them to ask all the technicians, but none have come across this problem. Any ideas?