Hi, a Ford P0171 is a LEAN code for cylinder bank 1, and P0174 is a LEAN code for cylinder bank 2. These codes commonly occur on many Ford vehicles, and are set when the powertrain control module (PCM) sees the air/fuel mixture is running too lean (too much air, not enough fuel).
When the Check Engine Light comes on, either one of these codes, or both, may be found when a code reader or scan tool is plugged into the vehicle diagnostic connector. IF the vehicle is driven long enough, typically both codes will be set.
A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.
A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).
If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.
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Rouigh Idle is bad motor mount/ check all 3 /po171 lean bank/ not the same problem/ common 2.0 split port. Get a diagnosis plug in / check for vaccume leaks etc. Look under bottom for melted vac hose etc/ went thru month of agony/ BAD MOTOR MOUNTS.
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