Q: It's running smoothly, but all of a sudden it will stop, even if you're stepping on the accelerator, it doesn't moving at all.

Hi there. Since the vehicle is new and it is not moving when you step on the accelerator, first make sure that the transmission is in gear. If the transmission is in gear, make sure that the parking brake is not on. If all of the brakes are off and the vehicle still does not move when pushing on the throttle pedal, then there could be an issue with the throttle pedal. There were many different automobile manufactures that had replaced the throttle pedals in the vehicles for the same reason and was a Recall. I checked, at this time, there are NO Recalls on the 2016 Kia Rio. Depending on how many miles are on your vehicle, I recommend taking your vehicle to the dealership if it is under the Manufacture Warranty. If your miles are higher than the Warranty, then seek out a professional, such as one from YourMechanic, to help you with the throttle issue.