Why is my Polo 1.6 classic 2004 misfiring?

If it has been misfiring and assuming the check engine light has been illuminated start with having the code(s) read by your local auto parts store at no cost to you. The code(s) will help you determine which cylinder(s) is/are misfiring so you can start the diagnose process. It could be a spark issue or a fuel issue or even a mechanical issue. So start with the codes then repost info.