Hello. I had the same problem as you with MKIII 16V. Stalled randomly when clutch depressed and revs up and down manically before hand. If you go to sites like this you will see hundreds of requests like yours and an equal amount of answers. I went through loads of things - relays, filters etc, with no result. I then cleaned out the throttle body, which is dead easy - just need a new gasket for 60p. After that no more problem. I couldn't believe it cause I had spent money on other parts that i prob din't need. Having said that other things worked for other people so I would say that the best advice is go and get a list of things it may be from various VW sites and start with the cheapest.
PS- the throttle body didn't seem that dirty when i took it off, but hey my car now works - 2 min job.