So my Service Engine Soon light came on Friday night. Prior to it lighting up the car was running rough. It would idle normal then all of the sudden drop around 150/200 RPM and shake a bit then rev back up to whatever it was idling at (500 or so). Would happen once or twice at a light but never tried to die but stumble.

Once the SES tripped things changed and now it idles at 1000 RPM with no stumbles at all. Codes are P0171 and P0174.

Tonight I disconnected the battery and with the hood open I fired the car up and noticed no SES but could see the stumbling idle and heard a very loud hiss coming from the left side of the intake manifold. Air pump? Reason I am asking is because I cannot recall the last time I had it running with the hood open but the loudness of this hiss would suggest something is up. I shouldn't be hearing what sounds like a leak but upon looking could not feel any air being blown out. Odd.

Car will probably go to Nissan for a diagnostic and from there I can either tackle it myself or have them do something but that will be in due time. Prefer the DIY method.

 

If you used the online code decoder, on the forums here somewhere, you'll figure out really quickly that it is not leaking air, but rather sucking air from the atmosphere.

Those codes are for a lean condition on both your banks. A focused smoke test will help determine the location.