This certainly sounds like a typical inlet manifold water leak problem. The symptoms of rough start up and steam from the exhaust point that way. This happens more with the plastic inlet manifold than the later/ better alloy manifold but it is not unknown for a later manifold to give problems. You might also be able to see coolant stains below the inlet manifold.
An easy way to tell is to take out the spark plugs. No.4 (normally) will be unusually clean.
Of course there is the other way for water to enter the cylinders, i.e. HGF