The knock sensor is going off because of extra noise coming from the backlash in the valves. It's a common problem for the Sportage. Typically you just need to adjust the backlash on the valves so there is less knock. Not a very hard problem to fix, but it will return over time. It's a known issue that KIA has no fix for other than continuing to adjust it until you are out of warranty. Then you just get to deal with it, adjust it on your own, or pay them to adjust it. It has no ill effects on performance, just over time it makes a ticking noise until the engine gets warm. Then it goes away. However, the code does not and your little light stays on all the time.

Logansportage <img src="/forums/images/graemlins/patriot.gif" alt="" />

Thanks for the explanation Logan.
Can you please direct to the instructions how to adjust backlash in the valves?
Is there information about it in the service info at Kia tech info?

Thanks,
Lior