hey Scotty I got an 02 lincoln ls v6 i got a p0171 and 0174 I replaced both upper and lower Intake gasket and still get the code and idles horrible. I spray brake cleaner on cylinder 2 injector and idles fine. now could it be the injector o ring going in the intake leaking air. thanks Scotty

could be tons of things, from a weak fuel pump, bad maf sensor, vacuum leaks somewhere ese, or clogged injectors. Good Luck