Recently my car has started to idle roughly and stutter for the first 1-5 minutes depending on how cold it is and how cold it is outside. Once it warms up, I can switch off the engine and turn it back on and it's smooth and there are absolutely no issues (at idle, driving or WOT).
I have changed all spark plugs and coils several months ago as a preventative measure as I bought this car second-hand about 7K miles ago and had no idea how old these parts were.
Any ideas on what this could be theoretically at least?
Injectors and HPFP are a possibility, but why would everything work perfectly once warm? I do not experience any long cranks even when cold by the way.
Carbon buildup is a possibility I would guess, but again it seems weird that the problem goes away once the car is warm.
Codes-wise I get misfiring on cylinder 4 and 6 (and once I had 5), and I also get the misfire on multiple cylinders code.
I took a look at my "new" plugs and they do very much look like this guys:
Having said that, I took a look at the plug from cylinder 1 (which reports no problems) and it too is blackened.
Does anyone have any other ideas or thoughts in general?