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P303 Misfire

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So the car overheated a few weeks ago. It dumped the coolant from the lower Rad hose and I had it towed home. I put the hose back on, filled it with coolant, and drove for two more weeks, about 1,000 miles. The other day it started misfiring on the way home under pretty normal driving conditions. It threw a p301 and p303. I took the plugs out, cleaned em up a little as they didn’t look too bad, put em back in and now only p303. The coil on cylinder 3 had some rust and separating layers. I replaced with an oem coil. Still misfiring. It’s worst at idle, and if driven runs almost perfectly fine above 2700 rpm. Any thoughts?
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possibly warped head and valves wont seal. I would suggest doing a cylinder leakage test. From my experience misfire at idle/low load is usually a compression issue. I've seen a couple cars overheat so bad that the valve seats actually fell out of the head. but since your misfire goes away at higher rpm I doubt that's the case for you and a resurface and valve job should cure your problem if what im thinking is true
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