i have 2 ideas of what it could be. the first would be a bad maf. i've got a boxster, and when my maf was bad it was showing the same systems. after riding with the bad maf for about a day, the dme (ecu) finally put itself into "limp mode" and started shutting down cylinders. i'm not sure if you can do it on your car, but if the maf is bad on a boxster, you can unplug it, and it'll run fine (letting you know that's the problem of course). it's kinda weird, that's the first car i've ever known to do that...maybe it's an EURO thing....try it! my computer is setup to hold i guess..."standard values" that it will run off of, without the maf (NOTE: IT'S NOT A GOOD IDEA TO RUN LIKE THAT FOREVER IF IT WORKS).

i would also check your ICM. i have a buddy who worked at vw, and he told me that the icm is sometimes known to have issues. he said it's on the airbox, and they get wet a lot, causing them to short out intermittently (mostly with a lot of road vibration). he did say they usually have the dead cylinder at idle too though...not just with throttle response, but it'd be worth it to check. he said just try wiggling the plug at idle, and see if the cylinder you're having problems with starts acting crazy.

hope i helped-
stephen