Volvo: Volvo S40 Turbo 2006, volvo s40, intermittent problem

Question
My daughter's car has been having problems with misfires.  The check engine light came on and when brought in the code was for misfiring.  They could not find anything wrong with it.  It seems to be an intermittent problem.  All they did was update software, but I wonder if this will solve the problem.  Have others found this to be a problem.  It happened earlier in the year, in January as well.

Answer
Neal,
The last couple of S40's I had for the misfire I replace the coils, wires, plugs. So far all is good. Did the codes state a specific cylinder? The last one I did just said misfire. When I pulled the plugs and found #4 to be filled with oil at the coil. That cause the misfire... That plug was also bad.