Hi all , my 79' f350 has been running rough at idle with a slight miss.
One night while tinkering I noticed blue sparks arching everywhere !
Got new plugs and wires , fired it up ran perfect! But slowly it started
Running rough and missing again? Any ideas? Something with the electrical/ignition
System or something internal ?confused thanks for any help

 

If its been awhile distributer cap and rotor is a good place to start.

 

One thing to double check is plug gap. Excess gap will increase voltage. Also quality of plug wires varies a lot. With parts store wires I always go with the at least the "premium" variety. On my dent I have Bosh wires from AZ.

Last suggestion is to check it at night again. That helped me track down a cracked coil once. I couldn't figure out what was wrong, it had stalled, and I was under the hood at night. Got it going and saw the blue sparks coming from the coil. New coil and it was fixed.