S40 Reduced Power Rough Running

I had a similar problem with my S40. Reduced power and rough running were the first signs. Does it feel like an engine misfire? I eventually traced it back to the intake manifold flap. Is it throwing any error codes? A faulty switch for the intake manifold flap control could be the culprit.

Misfire is a good way to describe it, yeah. I haven't checked for codes myself, to be honest. Where exactly is this switch located, and is it something I could potentially fix myself?

While I understand your inclination to attempt a self-repair, diagnosing intake manifold issues can be intricate. A defective switch for the intake manifold flap control does align with the symptoms you've described. Given the potential complexity, and considering my own experience, I would recommend a visit to a reputable workshop. It cost me 465€ to have it sorted.

Thanks for the advice! Sounds like I'm dealing with the same gremlin. I'll bite the bullet and take it to a workshop. Turns out it was indeed the intake manifold flap. Got it fixed for 465€, just like you said! Runs like a dream now.