I just had my o2 sensor replaced the one off the exhaust manifold before the cat. The mechanic hardwired it in. now my check engine light is on again and its throwing the p0171 code Running too lean. I looked it up online saide it could be a bad MAF sensor connection and to clean all the intake sensors and reconnect them. I did that still didnt solve the problem. The next solution was to replace the fuel filter so i did that. I have the flexfuel model. Still is running lean throwing the code p0171. I checked the intake and its all connected and tighten down. Any ideas what else it could be?
2002 Gmc Sonoma 2.2 FlexFuel auto single cab SL 2wd

 

try pulling each of your injector wires off one at a time while the engine is running to see if it makes a difference on how it runs if one does not change how it is running you may have a bad fuel injector causing the problem

 

The Haynes manual is saying your means you fuel is lean. Also when a sensor triggers an engine ligt that means 90% of the time the sensor is doing what it is specified to do and does not mean the sensor is bad. Definitely have your fuel injectors tested along with wires.

 

My mom's 97 Bonneville was doing the same thing and it ended up being a vacuum leak on the throttle body. One of the rubber 3 way fittings had a split on the bottom side of the big connection that connected to the throttle body. The Mass Airflow Sensor was reading what was going into the engine but the split was letting in air that the sensor wasn't catching causing the lean fuel code. Take a can of Carb cleaner and spray all of the vacuum connections into the intake or physically put your hands on all of the fittings, that is how we found it. I hope this helps.

 

To lean not enough fuel. (volume) check the fuel pressure at idle and under load. Tape the fuel presure gauge to the windshield. and go for a ride. see what the presure is. If everything checks out you might have a voluime problem.