C4 Manifold Pressure Sensor Issue

I had similar symptoms on my C4. The ECU uses the manifold pressure sensor to measure air pressure, which is critical for calculating the air-fuel mixture. If the sensor fails, the ECU can't regulate fuel injection, causing reduced power and increased fuel consumption. Did you check the sensor's wiring and vacuum lines? A loose connection or cracked hose could be the problem.

Thanks. I visually checked the wiring and vacuum lines, but didn't test them thoroughly. Can you explain the specific checks I should do on the sensor and vacuum lines to confirm the fault?

Given your symptoms and what you've found, it sounds like a faulty manifold pressure sensor or a vacuum leak. You could test with a multimeter or smoke test the vacuum lines, but a workshop assessment might be best, considering the complexity and the sensor's cost.

I took the C4 to my mechanic. The manifold pressure sensor was faulty, like we thought. Repair, including sensor replacement, cost 235€. Thanks for the help; it made me confident to get it sorted quickly.