Slight misfire

[Golfgti5]

I have a 2006 Golf GTi. It has developed a slight misfire. Only happens at low revs. If you drive normally you can feel the misfire, once you put your foot down it disappears.
I have run a diagnostic and it says misfire No2.
I swapped plug and coil pack for No4 but No2 still misfires.
I then removed the intake manifold, disconnecting the fuel pump, 2 x fuel lines and all the bolts.
Then replaced the injector on No2.
I now have a misfire on all 4 cylinders, but the car runs exactly how it did before.
I then did a pressure test on all cylinders, all of them were 175psi give or take 5%.
My last test was a smoke test, all was well but i was getting smoke coming through rocker cover breather.
I am now a bit stuck as where to go from here.

[mjmallia]

Did you carbon clean the valves when the manifold was off?

Did you change all the injector seals also as they are one time use.

[Weedus]

Hey, i have the same issue on cyl 4.
Switched spark plugs and coils but the misfire was still at 4.
Ordered an injector, removed the intake to also do carbon clean and saw that the inlet valve was burned/leaking :(
No issues driving, dont feel power loss only misfire at idle... good luck ✌️