I have a 2010 Audi A4 2.0 liter engine. For whatever reason on my way home the car started shaking and the EPC light came on. The next day I took it to autozone and it said cylinder 4 misfire. So, I changed out all the ignition coils and spark plugs. Car started running beautifully. It ran for a full day, then on my way to work this morning it started shaking again and the engine light started flashing and then the EPC light came on again. Any idea what it could be?