Fuel Trim @ Idle	Fuel Trim @ 2500	Possible Causes
Rich(positive)	Good(Near 0%)	Intake vacuum leak after MAF
Good(Near 0%)	Rich(positive)	Low fuel volume
Rich(positive)	Rich(positive)	Low fuel pressure
Lean(negative)	Good(Near 0%)	Contaminated crankcase
Lean(negative)	Lean(negative)	Leaking injector or other sensor causing excessive fuel

Note:

Rich means the PCM thinks it needs to add fuel by increasing injector pulse duration. The AF/O2 sensor senses too much oxygen
Lean means the PCM think there is too much fuel and is reducing injector pulse duration. The AF/O2 sensor senses too much gasoline