A simple explanation is that your Nissan Versa's idle setting might be too low to allow for engine idling at a stop. Your Versa has a computer controlled engine which is supposed to maintain proper idle. If for any reason the computer receives inaccurate data from any emission sensor, idle speed may not be accurate.
The first thing which should be done is a quick visual look over for disconnect or broken vacuum hoses and electrical connections. Fuel pressure and fuel injector operation should also be checked. If it's found that no mechanical faults exist, a smog technician can then diagnose your Nissan Versa's computer system.
