My Peugeot 807 diesel loses power and belches smoke - is this a DPF fault?

I have a 2003 Peugeot 807 2.0 HDI. Every 400 miles or so, the car will suddenly lose power when driving and stutter intermittently for the next ten miles. When idling the engine will hunt between 600 and 1400 revs and, in urban driving conditions, the car judders badly and belches out clouds of black smoke. On the motorway, the fault is only detectable by momentary losses of power. No error message is displayed on the dash and after a few miles the car resumes normal driving. My garage has replaced the air mass sensor and blown out the DPF, to no avail. We presume the car is carrying out some form of maintenance cycle, which is malfunctioning. Can you tell us what's wrong?
It reads to me as if it's trying to regenerate its DPF, but if the system has run out of Eolys fluid that just won't happen. These people do a kit:

The stuff is caustic, so the job has to be done by a professional who knows what he is doing.
Answered by Honest John on

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