I have a peugeot 306 turbo diesel. It has 60k from new and my sister had it from 6months old. Problem is that when I had it a while I got a big puff of black smoke whilst doing 70mph for some miles on the motorway. I asked the AA man he said its more than likely the EGR valve. On the return home I noticed a massive lack in power. The car has a new catalyst as that went, and has a new exhaust as of last week. I still have a massive power loss and have no idea what to do or what the problem is. A lot of people have said it could be this or ir could be that but no-one is sure!
Take it imediately to have it diagnostically examined. They will plug it into a laptop type machine and will find what is wrong with it in no time.
I'd look towards the turbo - Its very similar symptoms to turbo loss. Dont drive it normally as if the turbo goes it usually revs highly, smokes massively and takes your engine with it. Mosts diagnostics will do the job at your home - have a look in the Thomson Local or Yellow Pages.
Thanks for the advice, went to peugeots, they were very evassive, 'could take around an hour possibly more and its �86 per hour!!!' The symptoms you have described are very helpful, I had a friend who had the rough running, masses of smoke, but, mine doesnt seem to have the problems peoplepeople usually go for. But I have been given a contact for someone who is very good with diesels and has a diagnostics tester. Thanks for your help very helpful!!