I have a 2007 vw gti with 360k miles on it, about 2 months ago i got a misfire issue that popped up and cleared up on its own. I took it to autozone got codes read they said random multiple misfires, and something to do with cam timing. I had it towed to a shop that specializes on these vehicles and all they got was code p0303, 2181, and 0036. However I did have them replace the timing belt and water pump service done which was 3k miles ago and car was running fine. They said that p0303 was due to leaky valve cover gasket fouling plugs as well.
2 days ago i got the p0303 code and car was running like crap and sure enough the problem dissapeared on its own again and no code p0303, I did however swap coils in the event the problem re occurred i could track it down. Well today it happened again car was running so rough engine shook so hard it unplagged the maf connector but sure enough misfire code stuck to cylinder 3.
So based on the logic that the problem did not follow ignition coil tells me it is something else.
What should I be looking for and how would i test?