I had the same sort of fault with my 1st R, basically i had an electrical fault with a wire from the ecu to the ignitor pack, i disconnected this from the ecu, when i plugged it back in my revs were always at 1300 - 1500 rpm.
I just thought it may need a fault clearing from the system or the basic settings reseting?
Im not saying it is that but maybe take it to Nissan and get them to quickly hook it up to the computer and have a look??