Yeah, don't worry guys - i won't be pulling out bits of the car left right and centre, it's going to the mechanic. Already have a good mechanic too - they have done plenty of good work on my previos car (a lot of times for free) and have seen the GTST a couple of times, although not in relation to this problem. I just wanted to get an idea of what may be wrong with it before i go.
I thought the fuel consumption was pretty bad myself, but as i said in my original post most of the threads on fuel consuption dont actually give a good idea of what it should be just the fact not too expect anything too high. I really wouldn't have bought a skyline if i was expecting to get 100kms for 5 litres of fuel, and would you beleive that this car actully has a better fuel consumption than my prevoius car (a very old E30 with a bucket of mods).
Anyway i'm now 100% sure of the fact that my fuel consumption sucks compared to everyone else here.
WazR32GTSt - thankyou for the straight forward advice, it is much appreciated.
I'm not that mechanically inept by the way. It's just that both Japanese and turbo cars are a different direction from what i'm used too.