Something along those lines. You'll have to drill into the tamper proof plug if someone else hasn't removed it yet.
Where does it say that? There is no where to set it using my Nanocom.
In the settings there is short term idle and long term idle setting but they are just the amount of steps that the motor has learned to maintain that reference speed. If you change them (on mine at least) they just go back to where they were when the ECU tries to achieve the reference speed.
http://www.nanocom-diagnostics.com/uploads/downloads/Lucas GEMS ECU Guide.pdf