The photo vehicle is 2005 NF Sonata with the dust cap removed.

Among many possible causes, one cause could be throttle body wire rubber cap found in conventional mechanical throttle body using the cable.

There is a dust cap like a brake bleeding screw cap as marked in the circle. However, as this rubber cap gets aged, it becomes brittle with cracks, the cap could fall off the throttle body cable and get stuck way down in the cable. This makes the throttle body wide open.

This situation can be very dangerous. The solution is to replace the rubber cap, temporarilly tape the cap to the wire or just remove the rubber cap.