Fault Code 16684

[kapowww]

Collapsed cat and head gasket leak sound scary..

Well I drove my car to the dealer this morning (different issue) and when I got there I did a scan and this time it had the same fault code along with saying Cylinder 4 [16688] was misfiring. I actually got this fault code the first time as well but I accidentally opened the Shareware version of VCDS and it gave me 16688 - Shareware Version so I didn't bother looking it up and only realised it refers to cylinder 4 as well.

I'll probably take someone's offer on using an old coil pack to test..

What confuses me is that since it's only the one cylinder throwing the fault code it makes me think it's a coil or something for that cylinder. If it was different cylinders throwing the codes then I'd think MAF or fuel pump, etc.. But I'd think that each time I'd turn the engine on/drive it'd throw the code, not just intermittently. Guess I haven't driven enough to notice a pattern.

Also when the engine is idling I can hear a periodic whoosh of air every couple of seconds.. Air/fuel mixture not getting ignited in one cylinder or wishful thinking?

[kapowww]

Replaced coil pack 4 with a working one and it's now fixed! Now I'll go and buy a whole new set.. Seems like $180 delivered for a set of 6 from ECS tuning is the best I can find at the moment. Anywhere else?

By the way thanks to Peter Jones for giving me a used coilpack and to Coralon for offering =] Very helpful people on this forum..