I have a 2002 chrysler neon le 2.0L non magnaum and i pulled the codes and I am getting the code P0171 and the fuel milage is really horrible. The neon only hesitates when unload and at the lower rpms. I looked at the spark plugs and the neon is running lean. I have changed the plugs, wires, runned the fuel ejection and fuel system cleaners through it. What are the possible causes that would cause the neon to run lean?

 

There may be a problem with the oxygen sesnors - yes I wrote sensors (plural). There is one at the exhaust collector and one in the middle of the catalytic converter.

Oxygen sensors tell the computer if the car is running lean or rich and the computer adjusts the fuel injection trim to compensate and run the ideal 14.7: air to fuel ratio. Other factors (sensors and other inputs) help determine the fuel injection pulse widths (amount of fuel at each injection), but the oxygen sensors are the main component.

Apparently P0171 is "System too Lean (Bank 1)" (Bank 1) ?? I don't know what their refering to there.

I'd take a look at the O2 sensors

 

I replaced the upstream o2 sensor and it solved my problems. Thanks to all the people that responded.