I have a2001 corolla with a code p1071.I was told to replace the o2 sensor before the converter.I replaced it and reset the light.The check engine light stayed off for 320 miles.It came on with the same code.The mass air flow sensor was replaced about one and a half years ago or about 20000 miles. Can you help me?

This is almost always caused by a failing mass air flow sensor. If you had it replaced with aftermarket you may want to replace with oem to avoild problems. Thanks P0171 Fuel System Too Lean (Bank 1)Possible Causes Setting Conditions Base engine "mechanical" fault affecting one or more cylinders Check for air leaks after the MAF sensor Check for air leaks in the Air Induction system (e.g., in the intake manifold) Check for air leaks in the exhaust manifold and in the exhaust pipes Exhaust leaks located in front of the AFS or HO2S location Fuel control sensor is out of calibration (e.g., ECT, IAT or MAP) Fuel delivery system supplying too little fuel during cruise or idle periods (e.g., faulty fuel pump or dirty, restricted fuel filter) Fuel injector (one or more) dirty or pressure regulator has failed HO2S has failed (it may be contaminated with fuel, silicone or water) Vehicle driven low on fuel or until it ran out of fuel