When I purchased my 07 it had codes P0171, P0174, P0430. Previous owner had installed an SLP X-pipe. I started down a long road of trouble shooting and info seeking. I signed up for a SCT tuner with an etune service, I data logged a bunch and sent in for review. Replaced all 4 O2 sensors, 430 gone. New plugs, MAF sensor, no change. Had the car smoke tested, showed an intake manifold leak, replaced intake gaskets and all new injectors. Retested with smoke, no leaks. Still codes 171 + 174. eTuner insisting on an air leak somewhere or something to cause air fuel mix to be not right, trims lean all the time. The fuel pumps always sounded funny at start up, replaced both, saw some fuel trim improvement. Still a huge imbalance. etuner suggested looking into the EVAP system. Compression tests normal, that eliminated a possible valve hanging up. I found a slightly leaking purge valve and a failed purge solenoid through vacuum tests, replaced failed parts. Fuel trims showed a bit more improvement but still pulling those codes. I tried a few more things but what ended it all was taking the car for a dyno with a guy that's been doing mustangs for 35 years. I gave him the list of things I had done and he thought about it for about 5 minutes, ran the first pull, made an adjustment, pull 2 better, then finished up with a 3rd pull. I asked what he found, his reply... cam phasors, you need 2 new ones. He adjusted things to make the computer happy until the end of the summer when I took the car back for 2 new phasors and a retune to set things right.