[Twinsteer2000!]

Crazy story. Started truck and loud clatter started at idle. All fluids are fine, has about 244,000 miles on it. Revved it a bit and smoothed out. A little higher and it popped like a miss and puffed a bit of blue smoke, not black. I've never had one do this, anyone else? Thanks in advance.

 

[ssteve]

Pull the valve cover and closely check all valves to make sure they are all moving the same amount. Chances are you dropped a valve seat or valve. Maybe you got lucky and the injector just stuck open, but you said nothing about white smoke.

 

[evildiesel]

A bad injector can also cause blue smoke at times. Do what ssteve says and pull valve cover to inspect.