In the sequence of my previous question about the engine vibration (Engine is vibrating when idle and seems like missfiring), I have been trying to diagnose the problem on my own. What I have found out is that there is a possibility of one cylinder having a weak spark. When I unplug the cable on one spark plug, I see no difference happening on engine performance, while when I remove the cable from others engine starts to struggle. I have changed the wire, but the result is exactly the same (well the situation has improved slightly, but still not much better). My next guess is it might be the rotor and the cap which needs a replacement?
Is there anything I can do to diagnose the problem?