i have a truck that when you start it first thing in the morning when its cold it misses out really bad and puffs out blue smoke, a while back the exhaust came undone and i drove it like 2 weeks with no muffler would this cause it to act up?

 

What engine,, how many miles on the clock?

No,, a missing muffler won't cause a misfire, or have causes the engine to smoke...

Does the engine 'smooth out' completely once warmed? Use oil ect.? No running issues other than on startup? No CEL? Does the smole smell like burning oil, or excess fuel? Any other info you can add would be of help...

 

Sounds like valve seals leaking oil into cyliders overnight, once oil burns off plugs engine smooths out.