have a 1998 lincoln navigator. runs rough at idle and sometimes dies. check engine light on indicates both banks lean upstream and down stream. changed o2 sensors, installed new fuel filter. no change. no apparent vacuum leaks. any ideas on what the problem may be.

I would check for "proper operation of" and/or codes relating to; #1 - the IAC (Idle Air Controller) or ISC (Idle Speed Controller) as these control the "Cold Idle" (which is a function of fuel/air mixture), and #2 - the EGR valve for proper operation.

I have a 98 Lincoln navigator and don't pass emissions because the machine shows code po174 bank 2 and po171 bank 1 somebody know which one For the fuel and the location because I know is 4 sensors but my truck is spending too much gas please help I need to pass emmision thanks