I recently bought a 96 I30. It had a bad rear valve cover gasket leak and there were fumes coming out under the hood when I drove the car oil was leaking from the rear of the engine on to the exhaust manifold. Even though I have not worked on any car before I decided to fix it myself, looked up youtube videos on how to do it. There are so many hoses, vacuum lines, invisible nuts and bolts to be removed. And after 10hrs of cussing, wrenching and slight lower back pain, I was able to replace the rear valve cover gasket. After driving for about 20-30 miles, the check engine light came on. I double checked all the wires and connectors I removed thinking I might have forgotten to put something back when I removed them for replacing the rear valve cover.

Do you think replacing the knock sensor P0325 and O2 sensor P0130 would fix my issue. The car runs and drives fine. Is there anything else I can check before I replace these parts?
Also I was able to get a wrench on the 02 sensor but its on super tight. I was not able to remove it. Do you think it easier using universal joint?

Any inputs appreciated.