Although you state that you have always taken care of maintenance on this vehicle, it is apparent that you did not take care of the timing belt replacement which was scheduled many thousands of miles ago. And, as another member of this board likes to say, your engine will run very nicely right up until the milisecond when the timing belt snaps.
When the timing belt snaps, one or more pistons will collide with one or more valves, causing major internal engine damage. Since the exact timing of that event is unpredictable, I would suggest that you have this long-delayed bit of maintenance done a.s.a.p.
And, if you want to continue to enjoy your Kia, I would suggest that you read and follow the manufacturer's Maintenance Schedule. It should be sitting in your glove compartment.