I found the following post on another website:

I am currently running a Peugeot Partner 1.9D (DW8 engine) for work, on 100% diesel, it has never seen anything other than pump diesel....

However, it has developed a fault whereby it will ALWAYS idle at around 1100rpm, regardless of running temperature. It used to run at 1100rpm on cold start and then drop to 900rpm at idle when warmed up, but this no longer happens. Since this fault has occured, it is also a lot slower than the other vans in the fleet which are identical, in as much as that it is about 5mph slower top speed, will not rev so freely, or over 4000rpm without a real struggle.

I am guessing this is all because it is now constantly always running rich due to being stuck on a cold start setting...

Any ideas on which components would cause this problem on the DW8, as I'm not that familiar with the engine setup on this...

It also sums up my Berlingo perfectly.

There never was a resolution, so I thought I'd see what the HJ hive mind made of it!