[jhirasak]

TKB,

From looking at the photos that you posted, it appears that you have had significant moisture condensation inside of your distributor in the past. This can lead to electrically conductive paths in the cap which sends some of the spark to other cylinders or to ground, hence the missfire and rough running.

The usual cause of moisture condensation inside the distributor is washing your engine while it is hot and any steam that has gotten into the distributor naturally condenses on the cooler cap interior surfaces. The best way to avoid this situation is to remove your distributor cap after you have washed and cleaned your engine and let it air dry for a while before reinstalling your cap. If you need to drive your car soon after you have washed the engine, then check the condition of the cap the following day and wipe any condensed moisture from inside the cap. This should prevent the situation that you have experienced from causing you problems in the future.

John