I presume this is the regular gasoline engine 2.4 L version, not the hybrid or plug in hybrid Optima, right ? If so, I see some bulletins for the CVVT unit (which I presumes mean “variable valve timing”) “cover” and “motor plug” (whatever that part is) . There’s a check engine light and diagnostic code (p0010) associated with this problem apparently. I don’t see anything about a sensor though. Maybe it is the camshaft position sensor, don’t know.
Engines with variable valve timing are extremely sensitive to oil degradation. Oil problems that wouldn’t even be noticed in cars where the oil & filter changes were deferred before VVT will be front and center with VVT. So keep the oil changed frequently, and only use oil that conforms to the specifications required for your car. From what I see that’s sae 5w-20, grade SM or better. Changing the oil and filter more frequently than the maintenance intervals manual recommends is probably your best bet. I wouldn’t go beyond 5000 miles with that car myself. Use a quality oil filter too. Ask the folks at Kia if they recommend a certain brand/model of oil filter.