P0171 Code

I have a 2005 Tacoma (V6 4WD) with a K&N cold air intake (installed in 2010). I got an oil change at the dealership a few weeks ago before going on a 1400 mile road trip. About 1100 miles into the trip, my check engine light came on. Took it to Autozone and they ran the diagnostics, finding a P0171 (Fuel System Too Lean - Bank 1). I don't really notice anything as far as rough idling, etc., but hopefully it doesn't get bad enough that I do. Most of the info I found pointed to the Mass Air Flow Sensor. I saw they can get dirty and oily (as a result of the oil from the K&N filter) so I decided to just remove the MAF, clean it out, put it back, and wait to see if the light goes out.
My questions:
-How long until I know if it worked or not?
-If I run the diagnostics again, what am I looking for?
-What screws can I get to replace the ones from the MAF? I may have stripped the allen key ones that came with it. I just don't know what size.
-What other things can I do/check?

 

It can take many many drive cycles to clear the light. Can't Autozone clear the code as well? Also it takes awhile for the fuel trim to re-learn.

The MAF is a suspect, but you have 2 banks, and both use the same air flow meter, this can lead to some mis-diagnosing. Cleaning it would be my first step if I were at home with no special tools.

Ideally you would work on while monitoring fuel trim levels and inspecting to see what affects it.

With lean on older MAF vehicles I usually look at things like vacuum leaks. You have 25 year old hoses, they can be brittle and leak.

Exhaust leaks, if a sensor or manifold is leaking, it will draw in atmosphere and distort the sensor.

Next the sensor itself, is it reading erroneously?

 

Fuel pump going bad can also cause this code. The engine may not run rough because the computer is making up for the lean mixture by adding more fuel to compensate. Thus, with this code, you may actually get worse mpg.

I recently had this code and found the youtube video below most informative about fuel trimmings. It was a vacuum leak in my case - I didn't tighten well the drain plug on my catch can when I emptied it - doh!

https://www.youtube.com/watch?v=5WnM_NsOtd8

 

Bishop, I agree first suspect would be vacuum issue, if that's not the case and please correct me if I'm wrong, but fuel is fed to the fuel rail through the bank one side, fuel injector on cyl. 5 on 1GR-FE usually gunks up first, heat kills em, maybe damaged fuel injector on cyl. 5, running lean throwing code from sensor on right exhaust manifold?

 

Yep, I would agree to some extent, we usually see misfires on Toyotas when the back injector plugs up (we had a 5.7 do that the other day) but it's always a possibility.

 

Thanks for the advice. So far, the CEL is still on (been 1 day and a couple of drive cycles), but I feel like my throttle is much more responsive today after having cleaned the MAF. I'll do a thorough check of hoses, as well.