I had the same problem twice, first time was the coolant temp sensor, second time was crappy plugs, just paid .99 for a new one (yes I run copper ones). If you can Vag-Com it and find out what cylinder it is missing on that can narrow your troubleshooting down.

 

I need suggestions please! 2004 A4 T 1.8 85,000 miles- issue misfireing when idle CEL is on and now blinking received codes p300, 301, 302, 304. changed out spark plugs, coils, checked MAF, check fuel filter/pump all okay...any ideas what else it could be???

 

Have you replaced the crank sensor??? I now it was mentioned in the beginning but i was one of the ones on here for days and went through everything that you have and come to find out it was the crank sensor... Car will run fine when cold heats up miss fires and if it gets really bad will die unless held above 3000 rpms.I got a bosch from autozone i think about 100 bucks not sure though...