[keitho64]

If the air oil separator has not been replaced that could be an issue.

I have an 00 C2 with 57,000 miles. It would intermittently spit/sputter, like a misfire, but never trigger check engine light. It finally did about 1 month ago and it was an up stream O2 sensor. I bought 2 new O2 sensors but the error has not returned so I am just waiting.

My car had the plugs, coils, valve cover gaskets and AOS replaced at 51,000.

It is also possible you have a leaky valve cover gasket that is causing the coil to arc. You can check by removing each coil and see if there is oil on them. If there is, I would bet that is the issue.