ok craig no cel light is not good sign means its most likely been chipped badly

with those mods it would need at the very least a decent chip or ideally a remap, blow off valve check that for operation too has it got a manual boost controller?
it does sound like the classic scooby setup just waiting for a big bang

edited to add the cel light will be disconnected because of the chip making it stay on all the time only problem is then if there is a problem u don't have a working cel light to warn you.
if there are no other obvious things wrong ie: pipes off ect then i would seriously look at getting a better chip, especially if its a old one, i have a spare early 4 pin ecu for £30 as well.
you need to find out which turbo it has td05 or td04 then u can get a chip to suit.