ecm

I have a 2001 gmc sonoma truck with a 2.2 liter 4 cylinder engine. Its throwing a code po171(bank 1 running lean). I have done all the checks I can do and when I clear the code it keeps coming back. I have changed the entire exhaust system with the 2 o2 sensors, I have changed the fuel filter the plugs and wireset. Now it is misfiring at a higher idle. What do I check for now.