Hello there , my first thought would be the EGR valve . These get covered in oily soot that builds up & can cause the valve to not cycle through its full range of movement . This can lead to loss of boost , incorrect fuelling and fouling of oxygen sensors in exhaust . Try & find a local indie who can read the codes . Does not need to be genuine Volvo , Snap-on / Launch or Autel are certainly up to the job .
Codes will lead you where you need to go & avoid wandering around aimlessly ,chucking money at the issue
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