WOW thats wierd! How did you dicover that it runs better with the the wires pulled lose?
The plug grounded on the rubber heater hose?
Did you use some kind of cleaner under your hood that that may have left a conductive film?
Try cutting the wire boots back alittle so thier like it is plugged in when thier pulled back.
Let us know what you find. This is a real head scracher. It has to be something simple. Bet when you find the problem it's one of those on sh!tter's