Hi Barry012,
Not sure if you solved the issue yet. I have A corolla 2001 with 180k on it doing the same thing. I checked for vacuum leaks, replaced air filter, replaced spark plugs, PCV valve, MAF sensor, Purge valve and finally put the techron concentrate stuff with no luck. I have an OBD2 Bluetooth thingy and i still can see my Fuel trims runing positive all the time. The car runs fine on idle not too great with gas in city only and sometimes hesitate going uphill and i smell some not pleasant fuems but nothing too serious. I thing i might try to hook up fuel pressure gauge ( it is not easy and messy) then replace injectors maybe. The P0171 code is caused by more air than fuel in the system and since you are sure there is no unmetered air going in then it is incomplete burning pushing more oxygen to sensors. That incomplete or not efficient burning caused by less fuel supplied or maybe weak coils? in other words a very minor misfire in one cylinder or more. I posted here but no responses so far.
Thanks!
