Not going above 2k RPM

[Niall]

Faultlessly? I'm sure I read a post about yours with a bad idle or something!?

Tom306XS had probs with his too

As did CAR.....

I've had a hunting idle but I've had that since day 1 of owning the car.
Tom306xs had problems with his exhaust manifold and that was because the garage who fitted it didn't fit the exhaust properly.
As to CAR, not sure what his problem was but I know a few people ran them with the gti injectors and that will run like shit unless you remap it for them injectors.