My 2010 Aveo with 117k miles on it has been all over the place this summer. Had a persistant P0420 code, wasn't going to pay for a new catalytic converter (had a misfire in January, so was pretty sure it was a failed converter causing the code) but also couldn't afford a new car just yet. Through the generosity of some friends, I got a new catalytic converter put on my car from a really reputable repair shop. Before they replaced the converter, they checked both of the O2 sensors for their functioning. About 24 hours after picking my car up with the converter, my OBD pulled up a check engine light reading P0138. I tried clearing the code, but it came back. The P0138 code has been consistent now for 2 weeks.
Is this definitely a failed O2 sensor? What else could cause this? The RPM have also been really slow to reduce to idle speed after starting the car cold (when the engine is warm this problem doesn't happen). Was thinking it could possibly be a clogged fuel filter? Any thoughts?? I'm moving cross-country from Chicago to Colorado in about a month and a half and am nervous about the car being safe to drive into the mountains