What causes a car engine to stall on idle and lose power?

It might just need a tune up. Pull the plugs, and check their condition, they can tell you a lot aboutwhats going on inside the engine. My guess is the air fuel ratio is probably off. So much so that tje computer can't compensate, and is throwing an o2 code. Check for vacuum leaks, check your TPS, plug wires, MAP sensor, ect.