Check engine light is on

I have a 2002 2.0 L subaru wrx turbo with 119000 miles on it and I have replaced the spark plugs changed the oil and all fluid levels are good car runs fine a little rough at idle but thats normal with the boxer engine right? But my check engine light comes on and I went to auto zone and I hooked up the computer and it says that cylinders 1,2,and,3 missfired and I clear the codes and it comes back a couple days later. What Should I do? Could it be the spark plug wires? I have NGK iridium spark plugs in it right now.