Seat Altea Diesel Engine Trouble

Sounds like a faulty manifold sensor. Had similar engine performance problems with my old Renault Megane. Check engine light kept popping up, power was down. Was a pain! Could be large vacuum leakage, but probably sensor failure.

Vacuum leakage? How would I check for that? Is sensor replacement something I can do myself or better left to a professional?

Checking for vacuum leaks can be tricky without proper tools. As for the sensor replacement, it depends on your skill level. It's usually accessible, but you need the right tools and knowledge to avoid damaging anything. If you're unsure, better to have a workshop do it. That's what I did in the end.

Took it to a local shop and they confirmed it was the manifold pressure sensor. Sensor replacement cost me 235€. Engine performance is back to normal now. Thanks for your help!