Some on start up could be bad stem guide and or a head gasket. Oil leaking into your engine can cuase dieseling if it is hot enough, and have actually seen diesel eninges run away with a bad oil leak into the cylinders. I would take it to the shop just for the dieseling alone. If it doesnt seem right what they tell you then contact another shop and see what they say. Usually if you get 2 saying the same thing then they might actually be right.