Intermittently plugged and/or leaking CPMI injector poppets can often occur without setting a MIL (malfunction indicator light). The linear EGR valve may also occasionally stick open because of balls of pure carbon wedged into the valve orifice. You should have someone retrieve the DTCs. They will be set in memory whether the light is currently on or not. That is the best place to start.
Jim O'Neill - Chino Autotech Inc., Auto Club SoCal AAR