Having worked as a Nissan tech in the past, most Nissan engines had a little roughness or vibration at idle. The VQ engines are no exception. I bumped my ignition timing advance by 3 degrees and increased the base idle to 750 RPM and it idles pretty good. It doesn't run as smooth as a Honda engine, but it's better than what it was before the adjustments.
How do we regular folks change those settings?