The P0171, P0174, P0175, are all lean codes. First thing would be to check for vacuum leaks, especially at the intake manifold upper/lower junction. The O-rings love to fail and suck in extra air which gives you a lean mix and will give you the codes you have.
P03XX codes are all misfire codes for each cylinder.
If you only had the 303 (cylinder three) code and got the others after a plug change you may want to check the plugs you used and the coils. But do that after you repair the intake leak.
Monday, December 21st, 2020 AT 1:46 PM