Is this a new C4? Also did the car go into "limp mode"?

BTW, it isn't due to use of bio-D.

I bought a new Peugeot 307 2.0L HDi (engine DW10BTED4), which might be the same as the C4, in Nov 2006, and I had a similar symptom about 6 months after purchase. I had also just filled up with bio-D when it first occurred. The agent didn't seem to have a clue about how to fix it because after two visits back to the shop it was just the same. I had to do my own research and discovered the most likely cause was a faulty exhaust gas pressure sensor - several other owners had similar symptoms which were similar to mine and they had the pressure sensor replaced under warranty. I took it back to the agent and told them I wanted a new sensor fitted and after that the problem disappeared never to return.