Peugeot 207 crankcase ventilation issue

That does sound suspicious. I had a similar issue with my older Renault Megane, though the symptoms manifested slightly differently. Mine idled rough and smelled like fuel, but the underlying cause was the same: a defective crankcase ventilation valve, which caused emission issues. Is there any unusual hissing sound, like a small leak, when the engine is running?

I haven't noticed any hissing sounds specifically. How did you diagnose the crankcase ventilation issue on your Megane?

The diagnosis was tricky. Initially, I suspected a vacuum leak, but further inspection revealed oil residue around the valve. Think of it like a faulty pressure relief valve on a water heater; if it sticks, pressure builds. For the Megane, I had to replace the valve. Considering your symptoms, the best course of action would be a visit to a workshop; a diagnostic scan would pinpoint it quickly.

Thank you for the information. I visited a workshop, and they confirmed a defective crankcase ventilation valve. The repair cost 360€.