C4 2.0HDi rough running and excessive oil from rocker air pipe

Hello all,

I have a 2.0 diesel Grand Picasso. It started running quite badly and juddering whilst driving. After investigation I discovered the air temp sensor was completely caked in dried oil. I cleaned it, replaced it and the car ran fine but it soon clogged up again. I was also getting a depollution error.

I tried clearing the DPF by running in manual at 3500 rpm but it forced the car into limp mode and gave a crazy range of errors including automatic handbrake failure and ESP.

I tracked the oil down to the rocker cover air pipe that joins the air system just above the turbo. I disconnected it, blanked off the main air flow and put a k&n style breather on the rocker hose. I then took it for a good drive in manual modein 4th gear at 4000rpm to purge the DPF and it ran fine.

The car now runs like a dream and has cleared the fault codes itself. So obviously the oil vapour was tripping the sensors and affecting the air/fuel mix.

My wonder is what can cause the excessive oil from the rocker? I spoke to Citroen specialist, they had never heard of it happening and said they could see no issue with my modification.

Any thoughts?

Cheers,
Steve.