There seems to be a problem with my STI. If driven average to hard, there is no problem, but on a light throttle it starts to hold back at around 3000 rpm and picks up when the throttle is opened wider.

It could be:
a) A problem with the fuel (97 RON with half a bottle of Rockoil boost) - hasn't given me any problems before, and goes well at full throttle.
b) Some water in one of the plugs - unlikely?
c) Sticking component in throttle body
d) A sensor misleading the ECU.

Any suggestions gratefully received ...

Dave