Replaced the plugs on my truck ('84 C10/350)a couple of weeks ago, and everything was fine. I has sent a post to this group ,needing help to locate the timing indicator. it turns out that when the engine was rebuilt, the indicator was never re-installed. Anyway, Yesterday, i was trying to adjust the idle etc., and the engine started running rough like it was missing. Not knowing what to do, I figured it was a vacuum problem. After HOURS AND HOURS of trying to solve the problem, I broke down and took the truck to the mechanic this morning. Well... $200 later... They said that I had 2 broken plugs. DUH!!!!. That was the first thing I thought, but did I chek them???? NO!!!. I figured, heck, I just replaced them a couple of weeks ago. I even had the timing light out and could have checked for spark on each plug BUT NO!!!!!!. Anyway, just wanted to share. At least the truck purrs like a kitten now. BTW, There was a vacuum leak, and there was no Dist. Adv. or EGR, so it was worth the money. Next time I will be a good boy and consult this list.... I just wonder how they set the timing without a timing mark.... Herman.