I have a 1997 4x4 4.6L F150 with 215,000 miles.
Last year when the weather first turned cold I got the code P0171 "System Too Lean on Bank 1"
I unplugged the battery and let the truck sit for a while plugged it back up (to clear the code) And it would stay gone for a while then come back. I never messed with anything since the truck ran perfectly and mpg was not affected. When the weather warmed up the light went away.
Last week the weather turned cold again and the light came on. I stopped at Advanced had the code scanned same thing P0171 System To Lean on Bank 1.

This appears to me to be directly related to the cold weather. Does any body know why the cooler/cold weather would affect this code?

I know the 02 sensors are basically seeing too much 02 which means lean. I am hoping it is as simple as a faulty 02 sensor. Maybe an 02 sensors gasket is gone and when it gets cold it throws the code? I haven't done anything but i bet if I disconnect the battery it will take 2 weeks before I see the code again...
This time around the truck idles just a tiny bit ruff... to me... My truck idles smoother than my dads 04 5.4 This truck has the smoothest idle of any vehicle I have ever been in. What I am saying is a ruff idle for this truck is smoother than most other i have been in.
I am a busy college student and any advice would be appreciated, Thanks!!

 

Check and clean the maf sensor.

 

Whups, I should of mentioned I have done that recently, the contacts are nice and gunk free.
Thanks...
anything else?

 

im havin the same problem but on bank 2 look at my posts and see if they will help you out any i cleaned my MAF sensor too but its still on i think its the O2 sensor cause my truck is doing the exact same stuff. no problems with anything but the check engine light comin on