Well to conclude the thread, the car went back for an inlet valve clean..on removal of the inlet manifold it wasn't to bad.. N20 engines don't coke up much compared to N55s and B48s..
We popped it on the dyno and she made a few more ponies and a bit more torque..quite common for these engines to adapt over a period to new steady state conditions..so mid range boost was up a little bit which gave it another 10 BHP and 27NM torque..
Should bring it back every 3 or 4 weeks..