Peugeot 407 water sensor fault

Oh no, that sounds like a pain! Water sensor issue... Is the rough running happening all the time, or just when it's wet outside? Have you checked the sensor plug for any obvious corrosion?

The rough running is intermittent, but it seems worse when it's humid. Besides looking for corrosion, are there other ways to test the sensor plug?

Okay, intermittent and humidity-linked definitely points to a wiring issue. To be honest, beyond checking the plug and wiring for damage, and maybe trying some contact cleaner, I would just take it to a workshop. Auto electronics can be tricky and you might end up doing more harm than good.

I agree about the electronics. I took it to a shop. It was a faulty connector, like I thought. Replacing it cost 95€.