What does emission test codes P0171 and P0174 stand for?

SOURCE: diagonostic trouble codes reported p0171

P0171 is system too lean bank 1, P0174 is too lean bank 2, and 302 is misfire bank 1. Look for vacuum leaks. If you don't find them, put a vacuum gage on it can check. The P0171 is almost always a vacuum leak. If not other possibilities are front O2 sensor is too old and should be replaced (if mileage is greater than 100k then replace). Try injector cleaner. Misfires are usually bad spark plugs, but could possibly be caused by insufficient fuel. I've never had a car of mine in bad enough shape to have that error.

SOURCE: 1999 ford taurus emission reading p0171 and p0174

just tune up ur car periodicly, clean filter. clean ur sparkplug.

SOURCE: OBD codes P0171 and P0174

Look on the passenger side of the intake at the rubber elbow attached to the big black plastic tube and then to the intake manifold. Make sure it is not sucking shut and maybe a small hole in the bottom of it.

SOURCE: CODES P0171 & P0174 EMISSION SYSTEM SERVICE

if you have the 3.8 liter its more than likely bad intake manifold gaskets or a cracked manifold. Ford has had several TSBs on this issue. O2 sensors do not go bad as often as mechanics say they do. I have a 1999 that after 100 dollars at the parts store solved all lean conditions on the top end. The manifold has three parts to it. A lower aluminum that houses the butterfly blades for the variable intake runners( known vacuum leak were rods protrude at passenger side of lower bad bushings likely cause). Middle riser which uses oring seals which dry out and cause major vacuum leaks. upper is more or less the top cover which uses one large oring to seal. Hope this helps!

SOURCE: how do i fix emission codes p1131 p1151 p0171

TSB
05-22-6
ISSUE:
Some 2001-2003 F-150, 2004 F-150 Heritage and 2001-2003 E-150/250 vehicles equipped with a 4.2L engine may exhibit the malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P1131 and/or P1151 (system too lean bank 1 or 2). This condition may be due to leaking isolator bolts/port gaskets in the upper-to-lower intake manifold mounting area. This condition is sometimes intermittent and may not be apparent on a warmed-up engine.


SERVICE PROCEDURE

Perform a self test. If DTC P1131 and/or P1151 are the only codes stored in the powertrain control module (PCM) proceed to Step 2. If any additional DTCs are present, follow normal diagnostic procedures found in the PC/ED Manual.

Remove the upper intake and replace only the port gaskets (9H486) and isolator bolt assemblies (9S479). The new isolator bolt assemblies use a rubber material that is green in color, do not install the old isolator bolt assemblies with the black rubber material. Do not replace any other intake parts or gaskets.
While the upper intake manifold is removed, check the exhaust gas recirculation (EGR) orifices that are pressed into each primary port of the lower intake manifold. If any of the orifices are plugged with soot, clean and unplug them with a pick and solvent.

PART NUMBER PART NAME
1L3Z-9H486-AA Port Gasket
3F2Z-9S479-AA Isolator Bolt