Vauxhall Vectra Manifold Pressure Sensor Issue

It's possible. Those symptoms match a faulty manifold pressure sensor. Has the sensor been tested? A large vacuum leak could trigger those issues. What diagnostic codes are showing?

I haven't tested the sensor directly, and I don't have the diagnostic codes. Should I check for vacuum leaks before replacing the sensor? Where are the typical leak points on this model?

Vacuum leaks are a likely cause given the symptoms. Finding them can be tricky without equipment. Considering the car's age and what you've described, a workshop visit is advisable to diagnose the pressure sensor and any vacuum leak.

Thanks for the advice. I took it to a workshop as suggested. The issue was the manifold pressure sensor, likely caused by a vacuum leak as suspected. The total repair cost was 235€.