P0171 code

P0171 - System lean Bank 1 - Put a scan tool on it and watch the fuel trims. See if the issue is a vacuum leak (most likely), bad purge valve or other air leak by testing those as you watch the fuel trims. Check the fuel pump pressure as well, a weak pump can cause this.
Basically you need to actually see what the various sensors are sending to the ECM to diagnose this.

Coil packs and plugs will not cause a lean code. Misfires caused by those could however cause a rich code.