The ongoing saga continues...
The GSi has since developed even more bizarre issues. On Sunday I removed the rocker cover to replace the gasket and in doing so found most of the turbo manifold bolts were loose (as in a turn each) so tightened them up and all was well, no blows etc.
10 miles or so of normal driving later, it's developed what can be best described as a supercharger esque whine/whistle when it comes on boost. The best way to describe it, like a whining alternator pulley or similar. Thing is it won't do it when you rev it, it'll only do it on boost and it's seriously loud.
I've checked all the vacuums, checked for any splits and made sure no breathers and so on are trapped but all seems well. The car drives fine, boosts fine and has no eml issues so I'm a little stumped here... the biggest issue bing it only does it on boost, so it's nigh on impossible to stick my head in the bay when it's doing it.
Appreciate it's a shot in the dark but any suggestions gents?