Evening Trevor.

The most common reasons for high idle co are as follows:

1) Tested engine too cold so closed loop not actually active.
2) Fuel pressue wrong.
3) Cam timing wrong.

The above all pressume correct sensor operation of course.
(map sensor output drift is a common one, affecting idle pressure most)

If i can be of any assistance whatsoever please feel free to call me on Monday mate, happy to help.