Audi newbie

Hi all, I need to pick some expert knowledge regarding A4. I have owned my car for nearly 2 years now and it's never missed a beat, well until the weekend. I will give you events. Driving normally, never driven hard, I started a small incline and it started a judder misfire symptom, I could also hear popping I presume from the air box area, engine man was blinking. The car really struggled. I went straight to the parts shop and brought a coil pack as I have been told they are common. By know the car seemed to have cured itself. Next day I thought I would take it round the estate and try to find which coil was at fault. Nothing. Ran sweet. Tried again this morning and it started again so I switched numb 1 with the new coil and ran still the same did this method until I tried all 4. I am hoping this has ruled out the coils. Now it will start, run for a few minutes and cut out I can hear popping in the breather system ? I am a competent mechanic but new to these cars I'm from the escort era, I am old school ! I have recently serviced the car with all filters and new ngk's about a month ago etc. Any help would be greatly appreciated. Thanks Car A4 18t Quattro cabby 2004