A misfire can be caused by lack of fuel or a vacuum leak also. When was the last time you replaced the fuel filter? Checked for vacuum leaks? Crack in the intake tube after the MAF?
If fuel and vacuum check out, try a new PCV valve and recheck your wires. It is possible for a coil to lose one cylinder sporadically. If you have or can get a spark tester and install it inline between the wire and #4 plug, it will give you an indication of fire from the coil.
If fuel and vacuum check out, try a new PCV valve and recheck your wires. It is possible for a coil to lose one cylinder sporadically. If you have or can get a spark tester and install it inline between the wire and #4 plug, it will give you an indication of fire from the coil.