2002 Expedition Rough Ride
 

Hi,

I just recently started having problems with my Expedition. The engine seems to be misfiring, but I just replaced the spark plugs about a year ago. The car rough idles at stops and when it's in first gear. I changed the oil, transmission, the pulleys and pumps have been replaced, the fan is new, the air filter has been cleaned. The service engine light is still on and an OBD is reading "P0171 System too lean (Bank 1)" with the symbols CAT, EVA O2S and HTR flashing, and the car refuses to run normally. I don't know what the PCV looks like, and I don't know what else is wrong. The sensors are clean, and I use fuel injector cleaner every six tanks I fill. Can anyone help me please?