Something else to check... Magnecors can "seem" to be on correctly, but not actually engage the slots in the cap or the coil. I'd go through each one and make sure it is seated correctly. You might need to lift a side of the flange to allow the trapped air out to get them fully seated. The same goes with the plug side. They can seem to be on, but not fully seated. If your arcing, I'd bet this is why. The spark is looking for somewhere to go and it's arcing out to hit a connector. This would also, most likely, be the cause of your poor idle...

I'll take a pic and explain in more detail when i get home.
Clint