P0171 and P0174 Lincoln Navigator 1998

Question

I have a 1998 Lincoln Navigator, seems to run fine at speed, started idling rough when stopped and shows codes P0171 and P0174.
I replaced the Mass Airflow Sensor, now it seems to have gotten worse. The engine stalled at a traffic light last night. It seems to run well at highway speeds, but fuel economy has dropped from it's normal 15 MPG to 13.4 MPG during a 50 mile trip.

Should I have disconnected the battery when changing the airflow sensor so the computer can reset?

Should I be checking the oxygen sensor?
Should I use fuel system cleaner?

Answer 1

P0171 Lean fuel system bank 1

P0174 Lean fuel system bank 2

False air leak after the MAF is very popular cause for a lean idle condition, If it runs great at highway speed and satlls at idle , This is more of a EGR being at fault, If the EGR stays open at idle you can expect a rough idle and a stalling with a lean bank 1 and lean bank 2. With the vehicle at a idle and if it is running rough touch the EGR if it is hot to touch the EGR is open you can either clean out the carbon build up or replace the EGR. Check the EGR before doing anything else.