There are a few things you could try but at the end of the day you may have to just fit a new catalyst and dpf to reduce the emissions.
You could try fitting a new air filter, carry out an engine flush and fill with clean oil. Before taking it for a test you should also drive the vehicle a bit harder on a motorway to bring the exhaust up to temperature and try burn away any excessive carbon deposits.
These might help reduce emissions to a level that will pass but if not then you will have to put car back to original specs.
I've pretty much tried all this already..do you reckon a cat off a 307 hdi will fit my 407..i heard this might be a solution as my car is a bit messed up...also it goes into limp mode now and again but if i pull in and restart with the accelerator down full it revs out again ???
Not sure about fitting the cat from a 307 as I have never tried that personally. However if you can make it fit then it should work.
I'll have to look into that a bit more...whats most common fault for goinginto limp mode ?? but does come out after restart
Going into limp mode can happen if any fault code is stored. It is designed to protect the engine from damage. Causes can be bad connections, faulty sensors or even bad fuel.