OK so I came across this forum and it seems like we are having the same issue that others have. Car is a 2004 kia optima and has about 106k miles on it. Took to autozone and they said 1,3,and 4 are misfiring. I am not sure if spark plugs and/or wires have been replaced. This is my neighbors car. They said that car stalled as they were driving last night. Said it stuttered then turned off. They were able to turn back on a drive a bit more but then again it died. Then car would not start and it had to be towed home. Today i looked at it and it started fine and they were able to drive to autozone for the test. The yellow check engine light is on solid. Any ideas on how to fix? Should we just replace wires and plugs first?
Since you don’t know if it has been done, then it is now time to do all those maintenance items that you are not sure have been done. (All those items listed in the owner’s manual.
I would do the wires and plugs even if they were not quite ready. if that fixes it great, if not then you have a couple of things you will not need to check and they were due anyway.
Note: One thing that I strongly suggest is not on the maintenance list for most cars. That is replacement of the transmission (auto) fluid and clean it’s filter. Do it about every 30-40,000 miles
Since you have misfires in several cylinders, the wires and plugs are a good place to start. But in a car this old, of dubious quality, compression may be an issue. Buy the tool, a compression gauge, to test compression (you seat the gauge in the spark plug socket and have someone turn the engine while you hold the the gauge in place). Refer to the manual for correct compression, but you can also use the other healthy cylinders to get a baseline.