This is what the original plugs looked like.
Is it normal for 30,000km old plugs to be this black? I know that stock this engine runs rich but damn. The plugs were gapped to 0.65 mm. I gapped the new plugs at 0.7 mm.
Been driving this for 2 days now and all fluctuations and hesitation in power delivery have totally disappeared. Power delivery is very smooth now.
The bad stuttering under boost in low rpm 4th gear hasn't made an appearance either.