I have a kia sephia and I changed tth O2 sensor and everything was OK. The check engine light came on after 2 weeks and the code said it was a defective o2 sensor. The same one that I changed. I replaced the top one again and in the meantime, I changed the plugs(NKG) and the wires. The light is still on and I don't get enough power. It strugles to get to speed. At60, on last gear, it just revs with no power. I'm lost.