Peugeot 407 sudden unexpected reving

That can be caused by either too high engine oil or a faulty turbo.

If you've replaced the turbo you will need to clean all the oil out of the intake/ inter cooler system. When the turbo seals fail the engine sucks oil through them and uses it as fuel hence the rpm.

Thanks:- but the turbo was not replaced the mechanic put it down to a bockage in an injector causing too much fuel to be dumped into the engine. He is now suggesting a blocked DPF and recomending removal and remapping, however from your reply i am wondering if it could be the turbo?.

Does sound like it,s picked up and ran on it,s own oil ,particulate trap would not cause this .but turbo or inter cooler issue or blocked crank case breather could as could injector issue.

My money's on the turbo.
Take the plastic inlet pipe off then get your fingers into the turbo you'll
Probably find the the impeller has a lot of play in it..
If your fitting a new turbo make sure the oil feed and return pipes are clear or it'll
Be goodnight for it as well. :)