I'm not going to start a new thread, since there are already a million "P0171" threads.
A day or two ago I started noticing a VERY intermittent hiccup while cruising at mid-rpm, low load. Barely noticeable, just felt like a little gust of headwind or something. I noticed it about every 15 minutes or so today, and was going to check for pending codes when I got home, when sure enough the CEL comes on.
Other than the aforementioned hiccups, I have no symptoms--idle is smooth and even, vac at idle is 21-23inHg (no large or obvious vac leaks I can locate), no problems under load or in boost. I've only got a stupid narrowband sensor right now, so I can't say anything for certain about AFRs, but it's little "dance" hasn't changed at all. I've cleaned the EGR valve twice in the last 50k miles (at about 108k right now)
I had just cleaned the MAFS a few thousand miles ago, so I don't think that's it, but I cleaned it again today for good measure. Sounds like the next place to look is the primary O2 sensor?