I have had very good luck with my 98 sephia, until recently. The car began to studder like it was missing or something and the engine will shake violently while at red lights. If I put it into park at that point the engine will rev really high! I have changed the plugs (with Kia plugs) and the coils and plug wires. The engine still behaves this way, only not as much. When I first installed new plugs I used autolites and the local dealer said that they will not work in a Kia so he sold me a set from their part department. I have also replaced the fuel filter and the air filter, etc...Any help?