Have you taken off the rocker cover and had a look at the lifters?

If its got the mechanical ones fitted (which it should being a 16i) then they probably just need resetting. The 16i workshop manual says this should be done like every 3000 miles or something, so quite possible this is what you need to do.

The other option is to simply replace the mechanicals with a new set of hydros. Many people will tell you you cant do this and should replace the cam as well. but in reality unless its a high power engine its makes no difference.

In fact about 70% for the RSi guys on the rsi on tour forum are running hydros with no trouble at all.

An easy fix and wont cost you very much money, especially if you just adjust the mechanical lifters in there!!