It's odd that the professionals weren't able to fix your car. For sure clutch pedal sensor won't be a problem if you can maintain rpms by keeping your foot on the accelerator while operating the clutch. The problem is definitely elsewhere.

Maybe your best clue is the error code, mixture too rich and start searching for a possible cause there. For example evap system, injectors may be causing this. These are just ideas. Don't tell the mechanic what to do, just let them decide. Take it to Fiat service center instead.

Replacing parts one by one will make you spend a fortune on the car.