Common Ford engine error codes include P0171 and P0174. If the check engine light comes on, it is typically one or both of these engine error codes that are generated. They are lean fuel condition codes that mean the engine is sucking too much air or not getting enough fuel.
Excessive air inflow can be caused by a vacuum leak, a dirty sensor or, an exhaust gas recirculation valve not closing properly. If the problem is not enough fuel, the culprit may be dirty injectors or fuel filters, a weak fuel pump or a leaky fuel pressure regulator. The lean fuel mix error may be accompanied by rough idling, engine misfires, hesitation during acceleration and overall poor engine performance.
One of the most common causes for these error codes is a dirty mass airflow sensor. The only way to diagnose the sensor is to hook it up to a computer tool at a professional mechanic shop. If it appears dirty, however, it is simple to either clean or replace.
To clean the sensor, disconnect the air intake tube, and spray the sensor with electrical contact cleaner. Allow sufficient time for the cleaner to evaporate, reconnect the hose, and test the engine. The sensor can also just be unplugged and replaced.