I noticed y'all had a service bulletin for the '08-'09 Nissan Versa for the code p1421 was there one for the '10 Versa? I'm having the same issue with my car as of this morning. 4/23/14
If there are no intake leaks, check your air filter if it is dirty replace it. If your car is under warranty the dealer will fix the issue assuming is it not a maintenance problem like a dirty air filter.
if you are not under powertrain warranty, I would reset the ECU, the easiest way to do it is to disconnect the battery for 30min or so. Then do an idle air relearn, see link below
http://nissanhelp.com/diy/versa/projects/nissan_versa_idle_air_volume_learning.php
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