Hi Stephen, You say that the pump has been tested and given the ok, but the wiper sweep is varying from 0.6 to 2.4 volts, which would normally indicate a worn track in the upper area of the injector pump? We have had a few with this fault and every time it has turned out to be the potentiometer in the upper area of the pump, these wear on the track in the area of contact which is the 'position at idle' Does the car hunt excessivley when you move the power windows up and down or load the vehicle by putting the heated rear window or heater blower on? If so, I would almost certainly say that the pump is at fault, as all the one's that we have done have turned out to need a pump. Apparently the track wears in this position as it is the idle position that the sweeper sits on more than any other position, This is usually confirmed by the vehicle having quite high miles on the clock as well. Hope this helps mate, Gunner.