P0171 and P0174 codes mean Left side lean and Right side lean.
The Oxy sensors are NEVER the problem. It's the intake doing it.
Go to a Ford dealer and tell the parts guy what your problem is and they have a kit.
It's quite a job and not for the novice. Also, if you're going to do it, remove the deck where the wipers are for better access. Taking my time it took about 4 hours.
Did it last year and it runs perfect and no more codes. | 
