Replaced intake gaskets, isolater bolts, MAF, Egr and solenoid. New pcv valve and hose.

Question

Replaced everything associated with 171, 174 codes and still get service engine soon light.

Answer 1

When everything has been tried and a fuel trim lean is just too elusive, try this use a fuel injector cleaner adding into the fuel tank is also a good concepts, Usually a top end cleaning is what is commonly used, we where able to restore the fuel trim doing this