I am having the same issue on my 98 with 123k miles. I am getting a p0308 error code (misfire on cylinder 8). I have completed the following repairs but the error code still persisting and the car is rough when idle.
1. Tested spark plug coil (error did not move with coil)
2. Replaced all spark plug with Bosch Platinum+4 spark plug
3. Replaced valve cover gaskets
4 Replaced Intake manifold plate (behind engine) and the gasket
5. New fuel pump and fuel filter (for unrelated reason)
Despite all these repairs, the car is still rough when idle but otherwise runs fine when it's moving. What are the symptoms of a bad o2 sensor? Is there a way to test the o2 sensor?