Well, I am finally at my wits end. My 280,000 plus mile corolla 2006 has the p0171 CEL code. the car is in good condition. I change the oil regularly and rotate my tires (a deer did hit the passenger side fender in '08).
I have tried everything to solve p0171 problem. I have had the problem off and on since 2011. At first I would just disconnect the negative battery terminal to clear the code. However in April 2013, I made a concerted effort to solve problem. Below is the general chronological steps I have followed to solve problem.
1. installed new air filter
2. installed new fuel cap
3. cleaned MAF with CRC electrical cleaner
3. installed refur Cordone MAF (Autozone)
4. installed intake manifold gasket - Felpro (black)
5. installed intake manifold gasket - Toyota (orange) got rid of Felpro
6. replaced spark plugs with NGK 5464 and purchased new fuel cap
p0171 code went away until end of July 2013, then it came back ...
1. installed new NGK 5464 spark plugs.
po171 code went away until 828 miles, then it came back ...
1. cleaned orange intake manifold gasket
2. replaced refur Cordone MAF with another refur Cordone MAF (still in warranty)
3. replaced throttle body gasket
4. finally ... replaced upstream O2 sensor ...
I am bald so I can not pull my hair out. Thanks for any advise.