peugeot boxer 2.2 engine puma c engine problems

[Midenglandretrims]

hi all , I have a peugeot boxer which is a sevel van , My boxer has an intermittent fault which doesn't show a fault code , the van becomes very hesitant until it hits 3k revs , then the engine gets a surge of power and a roar . There's a definite different feel to its response when its like this . This fault can stay for around 2 to 30 miles , can clear back to normal on its own or when the engines restarted .
I've temporarily restricted the egr with a restriction plate with a small hole in to see if its the egr sticking , common problem I believe. Any help greatly appreciated.
Cheers ade