I have 2006 Jetta 2.0T. I had my spark plug and coils replace year ago. Now I am get CEL light on start up (sometimes flashing). I found out it is fine if I rev the engine for about 5 second after starting. I pulled the codes and it was alway misfire on cylinder 4. I read lot of forum about this. Most say bad plug or coil, eventhou I just got them replace. I am going to try to switch plug and coil 4 with 1. Another thing i hear is a bad injector. Is they a test I can do to check this.. if it is bad how hard is it to replace.
OR it could be a carbon buildup. I do have 140k miles on it.. but why only on one cylinder?