Focus Manifold Pressure Sensor Issue

I had a similar issue with my Focus. Have you checked the sensor readings with an OBD scanner? What values are you getting at idle and under load? Also, can you hear any hissing sounds that might indicate a vacuum leak around the intake manifold?

I did check the sensor readings. At idle, the MAP sensor reading seems unusually high, and it doesn't fluctuate much when I rev the engine. I haven't specifically listened for hissing, but I'll check that now. Could a faulty MAP sensor cause these symptoms, or is it more likely to be a vacuum leak affecting the sensor's readings?

Based on your description and the sensor readings, it does indeed point towards a faulty MAP sensor or a significant vacuum leak affecting its performance. Given the age and mileage of your vehicle, it might be prudent to have a workshop professionally diagnose and address the issue. Vacuum leaks can be tricky to pinpoint without the right tools and experience.

I followed your suggestion and took it to a workshop. They confirmed it was a faulty MAP sensor, likely due to a vacuum leak as we suspected. The sensor replacement and addressing the leak cost 235€. Engine performance is back to normal now.