2000 Saturn SL2 PO174 lean bk 2 // PO171 lean bank 1

Computer problem
2000 Saturn SL2 6 cyl Front Wheel Drive Automatic

We have a satun sl2 year 2000 w/ po171/po174 dtcs. Usually we smoke the intake and check for obvious vac leaks (none that we have found), Then both o2 sensors (pre cat) were replace by another shop. The code po171 went away after the o2 sensors were replaced, however the po174 returns after 3 drive cycles. Any help would be awsome! Thanks.