After many hours of head-banging I finally solved the misfire issues! I had previously compiled a list of possible issue that I used as a checklist for eliminating possible faults one by one.
Now, lets review the list of suspects from an earlier post:
- Bad coilpacks
- Bad gas (water etc.)
- Bad spark plugs
- Bad MAF
- Vacuum leak
- Low fuel pressure
- Bad crank position sensor
- Bad O2 sensor
- And several others.
From just about every post and article I read on the internet, coils and plugs were on, or near, the top of the list of usual suspects. I had previously upgraded coils and plugs when I tuned the engine to stage one back in november 2016, so I figured they were OK. I did fix a few vacuum leaks thinking it was it, but the problem was still there.
I then went on and replaced the following items:
- Spark plugs
- Crank position sensor
- O2 sensor
- Fuel filter
- MAP sensor
- PCV valve
- PCV check valve (pancake valve)
- Misc. check valves
As it is a 15-year old engine, most of these parts needed replacement anyway, so I figured this was a golden opportunity to get it done. Unfortunately it did not resolve the misfire issues and I was running out of ideas.
As a stroke of luck, I got a hold of four coils from my brothers 2001 VW Passat before he sent it to the scrappers. I threw them in there to see if it made any difference – and voilà – the engine purred like a kitten!
Lots of work, lots of parts changed and the issue was what everyone said it would be… Lesson learned, listen to the majority and change the obvious culprit first.