When I am looking at misfire at idle conditions, I look to my scan data for clues. I have had more than a few customers who's concern was a misfire at idle, when in fact the misfire was there off idle also. As engine rpm increase, a misfire can be masked as rpm increases. Now if you are dealing with a secondary ignition misfire, you will feel it both at idle and when under load with the misfire becoming more noticeable as engine load is increased. Depending on what scan device you are using will determine the accuracy of your misfire graphing/tracking. If you have performed a compression test, I would recommend doing it again. Conduct both a wet and dry compression tests. This will help in determining if your are dealing with a valve train issue or a ring sealing problem. This is also a good time to closely inspect your spark plugs. I have seen plug insulators crack due to spark plug socket fit resulting in voltage grounding to the head before it reaches the combustion chamber.
I would test and eliminate any engine mechanical issues as the cause of your misfire first. Next I would examine your ignition system for weak cylinder contribution...coil(s), ICM, plug wires, plugs. If you have eliminated mechanical and ignition from the equation, look at fuel delivery as the cause of your misfire. These diagnostics often require some equipment most do it yourselfers dont have. That doesnt mean you cant accurately diag your misfire, however it may be more difficult to isolate the cause of your concern. Best of luck.
