HouseCallAuto 4/20/2010Check the air intake tube for a vacuum leak, check any hose for a vacuum leak anywhere on the engine. It could also be a bad mass air flow sensor. Further, more specific tests requiring a full service scanner are needed to pinpoint the one cause.
Bob R. 4/22/2010P0171 System too Lean, P0174 System too Lean. The comment by Hous CallAuto is correct. There either is excess air getting into the intake after the airflow meter which is between the airfilter and the intake manifold, or the meter itself is defective or fouled by dirt from not replacing the air filter often enough. Look for cracks in the air intake bellows or any vacuum hoses. You can also purchase a special cleaning fluid for the airflow sensor at a parts store before you replace it.