Ford Repair: 2000 ford focus se with engine p, valave, vacuum line

Question
The engine light is on, the computer reading is p0171...(oxygen sensor). What exactly do I need to fix?  Please help!!!

Answer
the most common concern for this is a kinked/collapsed vacuum line. it is located behind the the throttle body. the hose is about 3/4" in diamater. it connects from the pcv valave in the front of the engine and runs to the the throttle body. if you go to you tube. yu can watch a video on how to replace your pcv valave. the hose you see them removing is the one that is leaking