Right first thing is you've posted in the MK3 section, should it have been in the MK2 section?
Anyhow, I had a MK2 GTI, which kept on doing this, intermittent it just cut out, and messing about with the fusebox, and it usually sprung to life,
what I learnt was that water somehow gets to the fusebox, causing this problem.
And it is a common issue on the MK2