07 Mazda6-Rough idle about 30 sec when start cold then fine.Drive immed getP0604

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If let idle smooth out before put into gear runs fine. If drive before smooths out drops OBD code P0604 (misfire cyl 4). Checked all 3 available cyl (4,5,6) and compression is good at 160, plugs are new and resistance is same for all 3 so don't think I have a bad plug or coil. I have switched plugs/coils and get same code/same cyl. If restart later with engine still warm no problem, idle is smooth, can drive immediately. I have also replaced dirty air filter, and cleaned throttle body and MAV sensor. Vacuum lines look fine, and no changes when spray with carb cleaner with engine at idle. No change noticed if pull vacuum line off EGR. I also have run seafoam and marval mystery oil at high concentration for 75 miles thru gas to see if injectors sticking. No noticeable difference. Looking for suggestions.