My car started running like dog crap about 2 months ago. However, when the engine is warm it seems to idle better, especially driving it around for about 15-20 minutes. I plugged the diagnostic code scanner into my ECU and it says all 4 of my cylinder's are misfiring. So I went and bought some new ignition coils and sparks plugs, all OEM parts. I changed those out, which was pretty easy considering the coils are wireless (distributor-less ignition). I checked online to see if the plugs needed to be gapped at all, which they didn't, yet my car still idles really rough. I cleared all the codes and they all came back. I even changed the air filter out for a K&N thinking maybe that would fix the problem and it didn't. I have heard it could be an O2 sensor. I have also heard that there have been a lot of Audi's my year with intake manifold problems. Has anyone ever had this problem?

This is what happens step by step. I start the car, when it idles it sputters and seems to make "popping" noises. Almost sounds like there is a hole in one of the manifolds. After the car is around 210 degrees, the idling gets much better, but it's still flaky. My RPM's bounce from 800 to 1000. After I have driven the car for about 15-20 minutes, the idling issue seems to disappear COMPLETELY. I've never seen anything like it. Could my catalytic converter have something in it that would cause back pressure and cause it to run like this? I feel like the check engine codes would tell me if it was on O2 sensor, not cylinder misfiring, am I right? Any help would be greatly appreciated. Thanks everybody!

It's a 2005 (not 2005.5) Audi A4 1.8T Quattro with 91,000 miles.