jetta 1.8t misfire on 3rd and 4th cyl.

Hi guys, I have a 2003 jetta 1.8T and the scanner shows misfiring on 3 and 4 cylinders.  Before I spend alot of money on coils and wires, does anybody know of anything else that could be causing the problem.  I replaced the plugs already.  Any suggestion would be appreciated.  Thanks Jack