Do not take the pipes off, I did that an it made it worse after a while, we had a new egr valve fitted, a new sellanoid valve, an it didn't solve it, even the mechanic was scratching his head, so he worked his way back down through the exhaust and found the mesh in the catalyst was clogged up, changed all that and it now runs better than ever, in total it cost 330 quid, which I didn't think was bad at all.
Parky, August 2010