I had this same sort of problem with a set of Bosch plug wires and #4 seemed to be the worst. All of a sudden the engine would start running rough and even a miss. You could jiggle the wires on the spark plugs and the problem would go away for a while. This seemed to happen almost right away when the wires were installed and just got worse.

What I found was that the inside of the plug contacts had turned green from the Gulf Coast humidity. You could clean that contact surface up and improve how the engine ran for a bit. These were not cheap wires and I returned them to the Euro-store who gave me a brand new set of wires. These were supposed to be a better set of wires. The plug contacts looked the same but the contacts into the distributor were better. Used the moisture sealer on both sets of wires and paid extra attention to the 2nd set of wires. This set developed the same type of rough idle problem after a coupe of months. You had to jiggle all the wires on the plug contacts to solve the problem instead of a regular suspect. Looked at the contact inside the plug and the contacts were green again. The coil wire and the contacts at the distributor were also tarnished and green when they were removed.

Got tired of the problem and broke down last year and ordered a set of Bougicord from one of the online sources. Used the moisture stuff just like on the Bosch and problem solved.

I know lots of folks have had excellent luck with the Bosch wires, but i will be avoiding them from now on.

Good Luck,

Paul