Okay, what did I do wrong?

[PRattenbury]

I started the engine in my truck, moved the truck outside, turned the idle way up again, and was going to let the cam burn in some more. I started to hear some valve train clatter, which lasted a couple minutes, ending with a clink sound and the noise went away. But when I lowered the idle back down, it ran like crap. Later in the day, I took the truck for a ride around my block. It ran like it had 200000 miles on it, chugging and so forth. Before I pull the valve cover, I am going to guess a rocker fell off a valve. They are stock stamped steel rockers. Cam is an Edelbrock Performer, quite mild. Springs are stronger than stock. The studs are screw-in. No guide plates. Anyway, there is a question. What did I do (or not do) that would have prevented this problem???