Best to post your question in the "Z Car" section of this website.
Anyway, you can try the idle relearn yourself, it may or may not be what is causing your issue but it couldn't hurt to try.
http://nissanhelp.com/diy/z/projects/ni ... arning.php
http://my350z.com/forum/maintenance-and ... edure.html
Or, a Nissan dealer can do it in a matter of minutes, they can just hook up to their Consult-II machine and do it that way.
You can check for fault codes with an OBD-2 reader, you can get one at any auto parts store or even Wal-Mart, eBay, Amazon, etc.
Prices of the coder readers range from $15 to hundred of dollars.