I have a '02 with a 4G64 2.4L I4 and had a similar issue with the misfiring (Cly 2) and sputtering at idle but not initially any codes with the 02 sensor. Changing the plugs resolved the issue (didn't change the wires) however I still was getting the check light, this time it was in relation to the sensor as well as the thermostat. I didn't change it as it was too much at the time and there didn't seem to be any ill affects like in your case. Then, of course, one day it refused to start up after running for about 20-30 min and took roughly the same amount of time sitting before it would start again. Didn't stress it to much since parking it at work 10 hrs made the wait easy. A few days latter the battery (used) apparently crapped out and a simple jump got me rolling but it did so 3 times in 5 days. Replaced it along with alternator (as it was a victim of the bad battery) but still the start up problem progressively got worse and needed to sit longer and longer (currently 3-4 hrs). I took it to the dealership for a diag ($99 US) and they advised the that catalytic converter (the 1st one) was considerably clogged up and causing what essentially seemed to be some sort of overheating problem and quoted $1200 US (parts and labor) since it's part of the exhaust manifold but they side noted 'off record' to remove it and 'bang on it carefully' until the debris started to fall out.
Not willing to pay that much and to avoid it reoccurring down the line, I've opted to swap it out for a 4-1 header made for the 3G Eclipse and eliminate the 1st cat all together. Haven't done so yet as the part in on its way as we speak. Hope this helps shed some light and i'll update if the issue is in fact resolved from this. Good luck
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