1999 Ford Taurus Cylinder mis Fire

I changed my spark plugs out a few weeks ago. In an attempt to visit with my family up north my engine light started blinking. I was able to limp home but before that I stopped at an Advance auto parts store to have them hook up their computer for a quick diognostic check. I know that this is only vague but it was a start. They informed me that #2 and #4 cylinders were mis-firing. Not knowing why at this point I thought that I would go ahead and change the wires. This did not help. I checked the spark in the #5 and compared that with #4. They both looked fine. At this point I am left with no other choice but to take it to a dealership. My question is this, what can I expect to hear from them?