CEL code 2177 won't go away! Asymptomatic

Hey all.
So a few months ago, the CEL came on, car wasn't running any differently, no power loss, same mpg, etc. but I had it read at Autozone as I don't have a reader. code came up P2177, system too lean at off-idle, right bank. I waited on getting around to it, but finally did earlier today, cleaned the MAF sensor, ran some throttle body cleaner through, listened for vacuum leaks, couldn't find any, but did a homebrew smoke test anyway, didn't turn up anything. Tried the propane test as well, nothing there either. I've heard the purge valve can cause issues like this, so I took it off the car and tested it, it works fine, open when powered, totally sealed otherwise, so I put it back on. Also put some fuel system cleaner in the tank. Car is still running perfectly normal, the only think I can relate to this code is that occasionally (read rarely), the car will have a rough start, bogging in the RPMs until I hit the gas pedal and rev it, then it's totally fine. It's never not started, and there seems to be nothing I can think of that relates instances where it has this rough start, it's all random - warm engine, cold engine, just filled up gas or not, doesn't seem to make a difference.
Anything you guys think I can try before going the O2 sensor/fuel pump route? I'm just about to go out and clear the code to see if it still comes on after a few miles.

Car deets:
2006 Mazda 3 Hatchback, S 2.3L
150,000 miles, regularly maintained.

A couple of times I found a small cut in one of the small vacuum tubing that plugged into a firewall connector in the Protege. A lean code/check engine light was the clue. Visually check every vac line as you bend it at its connector. It mat open up as the engine bay temps reach a certain level, increasing the vac leak.

since it has some good miles on it. I would run like 2-3 bottles of lucas fuel injector treatment. through it. 1 bottle per tank. Sometimes it takes a few to remove all of the buildup in the engine.

Cool, I'll double check all my vacuum lines and see if I can't find any small tears. After clearing the code, it hasn't come back on, though it's only been about 100 miles now. I'm still getting the occasional rough start though. I'll run some fuel injector treatment in my next few tanks, too. Thanks guys, I'll be back if it comes on again.

Code came back, unfortunately, after a few hundred miles. I checked the vacuum lines last time I posted, but I didn't find any leaky hoses. Will double check the vacuum lines and update.

You can spray the hoses with some starting fluid, and if the idle increases, there's your leak.

I did try starting fluid, as well as a smoke test, with nothing to show for it. In any case, flooding from hurricane matthew took the life of my poor 3 while I was on vacation in the form of engine knock after ingesting some water. Sorry to all future lookers, I never found a solution for the CEL.