There is a bug in the 350Z HR ECU (with the VQ35HR engine) that can make the idle control become faulty. This happens if you move the throttles with the battery and/or ecu connected. Its impossible to reset the idle speed which often goes up to 1500-1800rpm.
It should be possible to perform an idle relearn – this can be done with Consult II or via a timed sequence of operations often called “the pedal dance”. This often doesn’t work. Other options that people have suggested (changing throttle bodies, unplugging them with the battery connected etc etc) sometimes don’t work either. The final solution which does work is to fit a new ECU which can be very expensive.
We now have a solution for this problem and can reset the original ECU so the idle will be at the usual 700rpm. The only draw back at the moment is we have to switch off the immobiliser too (although we are working on this).
Previously to fix the problem one would have to buy a new ecu. With our solution this is no longer required.