Why does my Peugeot 407 run rough every 450 miles?

I recently bought a Peugeot 407 HDi and every 450 miles the engine runs rough for 10 miles/minutes, i.e will not maintain constant revs when cruising. When it's stopped black smoke comes out. After placing it in neutral/park it then runs smooth. This all ends after 10 minutes and it is great for the next 450 miles. Can this be something to do with the DPF cycle? No warnings are displayed.
It will be actively regenerating its diesel particulate filter, which involves injecting extra fuel into the engine. But it probably also has PSA's Eolys additive system and if it's run out of Eolys it will run rough during the regeneration. You need to get that checked. Unfortunately, unlike AdBlue, adding Eolys to a Peugeot is not a nice DIY job.
Answered by Honest John on

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