New leads perhaps!

[yoshi]

I've recently noticed that when driving just above tickover, foot lightly pressed on gas pedal the truck vibrates a lot & it feels as if a switch is being turned on & off really fast or like a plug breaking down. It seems ok when I press down harder on the pedal. I've fitted new spark plugs, adjusted timing & fuel mixture. It's running better & cooler but it's still there, when I looked under the bonnet in the dark there's a ring of light around the end of nearly all the spark plug caps where they meet the plugs Do I need a new set of leads? These Accel leads have only done 1100 miles. Sbc350 & HEI thanks