Technical Service Bulletin #01 09 01 2020103/1 says crankcase ventilation pipe cracked can give you misfire codes p0300-0304. replace pipe.

 

Troubleshooting to one side of the motor. If you have swapped coil packs from one side to the other and problem stayed on drivers side it is not the coil packs. You need to read out you coil pack wire harness. Check all three on that side. Connector to coil pack 4 pin 1-4, 1 being closets to flat edge, 2 and 3 in middle. Read pin 2 and 4 to battery positive and you should get a light or voltage indication. Pin 1 to engine ground turn key on and you should get correct battery voltage. If correct voltage is obtained then dissconnect all fuel injectors very important! Then connect a test light to pin 2 and 3 and active starter briefly and see if light flashes. if it does not flash your going to have to go to dealership and have them test your engine control module wiyh the VAG 1598/31.

 

Last nite a friend gave me some advice on what could be the problem. He said disconnect my battery terminals and touch them together to get the power out of the ECU capacitors and have it re learn the timing curve. The fact that the old belt was stretched and the new belt being itght could throw off the adjustment. So I did it. Only have driven about 20 miles or so today but I have no check engine light and no flashing CEL. Could this really have fixed it?

 

I'd check the crankcase vent pipe for sure (any un-metered are after the intake will cause misfires). I also had an issue like this with one of my vehicles. I changed so many things we never specifically found what did it. As far as the CEL after you cleared it, it usually has to go through two drive cycles (cold - 35mph-55mph-coast, then over again), someone correct me but i think misfires would come on immediately so its very possibly you fixed it. Good luck !