Now my windshield washers have stopped working and more worryingly, the problem I've had from the beginning is getting worse. When I press the gas pedal from a standing start, its very sluggish - doesnt really move at all. If I back off totally and get on it again its fine. Seems to be happening quite often now where before it was pretty isolated.
I have an 01 A8L by the way.

 

I can't help with the windshield wipers, but as for the loss of power, I once had the same issue. The problem was caused by a brake switch (not the technical term). Bottom line the brake switch or brake fuse, caused the car's computer to think the car's brakes were being engaged and thus disengaged the throttle and my loss of power. I had it fixed under warranty, so I can't tell you how much the repairwould cost w/o it. Once the brake swtich was replaced the issue disappeared.

[IMG]local://upfiles/52557/A327609000B94A1E998D3EF0801E635B.jpg[/IMG]

 

It's worth it to have the car scanned for codes. Not every code will trip a CEL, so it's worth doing. AutoZone will do it for free. Then you can get the codes, search them out on here, or post them up for assistance from others. That's the easiest way to try and narrow it down.