I was struggling with my S40 for some time. The same D4204t, 2006 but still EURO3 (non-DPF). It was nightmare. Tons of additives, sprays, cleaners.. changing every filter, oil.. checking almost every sensor, connecting all sort of DTCs readers.. Previous owner kept some servicing receipts etc. with one pretty recent receipt saying that EGR valve was replaced, so EGR wasn't my first choice and place to look, but eventually I did removed it, clean it, adopted again using VIDA with only slightly noticeable difference. When cold HE was still shaking, smokey(bluish ,whiteish and smelly) and choking or coughing(not sure which fit more). But when warm he was like brand new engine. I was confused and started thinking that I'll have to get used to that and give up, but then I saw that there are no receipts for fixing or removing the EGR cooler, so I did removed it and it was totally clogged with carbon and lacquer'ish sht. I did ordered used but clean cooler for few quids on eBay, replaced and he's running since then like new.
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