My daughter-in-law's 2001 Kia Rio starts running rough and the check engine light comes on. When we hook the code reader to it it says Cylinder 3 is missfiring. We have changed plugs, wires, firing modules and had the dealer check it. They want $800.00 to work on it. She has already spent hundreds of dollars with the dealer and still no better. What
do you think might be the cause?