Hi John, yet another speedy reply!

I have noticed a couple of things here, looking at my manifold there
is a blank rubber on a little tube coming off the manifold, unsure
what this might be but i saw a youtube vid of someone who has a long
pipe to somewhere else in the engine bay,
http://www.youtube.com/watch?v=prHkn9E-ElI

perhaps that is something to do with the hissing sound.

I have come from a mondeo and i can see some definite similarities on
certain components such as the throttle body (who's IAC are prone to
failure) and the tps and MAF are exactly the same as earlier mondeos!

I think that re: GSi that its more likely to be ecu based than
different cams and pistons as i would have thought that would have
made them very expensive to manufacture. I would imagine that the
throttle body and MAF are probably different and the fuel mapping will
probably be different too. will try to do some digging on this!

what kind of 626 do you have?