1996 Honda Civic Code PO171

I recently got the engine code po171 (bank 1 too lean). So as suggested by a mechanic, I replaced the map sensor, fuel filter, pcv valve, and sprayed down the O2 sensor with electric compononent cleaner. But the code is still comes up and im getting about 22mpg compare to my 30-31mpg before this code came up. Any other suggestions that you might think what the problem is? Thank you in advance.