Not much of an update, but the car wasn't running right and had been cutting out when revved at idle, so that was fun trying to find the fault.
In the end it was the air diffuser I had chucked away when I replaced the old hoses for the white SFS hoses. It took me and Graham (DCMS) about two weeks on and off to find the problem, however in the process it did give the S15 got a good haul over.
Changed/cleaned
MAF
Injectors professionally cleaned
Idle control valve replaced
CAS replaced
Compression tested (all good)
Spark Plugs changed
Smoke tested for vacuum/boost leaks
So after all that it was just a simple diffuser that sits after the MAF to stop the turbo blowing air back over the MAF which can cause over fueling. common problem with Top Mount setups apparently.
So with everything done and now running nice, I had to get the map checked again. DCMS has a good relationship with Jez at Horsham Development (plus I've meet Jez a few times and know he's a good guy), so I took it down there last month as I had a meeting in Reading to go it, so it worked out just right. On the rolling road and its now all remapped and checked over, its now running as it was around 340-350bhp
Jez did tempt me with a set of cams, but I fancy a new body kit next...