2005 Peugeot 307 egr circuit

HI i have only had this car for the last 3 weeks the worst i have ever had from a car.in my life .so far i have changed the fuel filter the high pressure turbo lines and the egr valve and still the code is p490 EGR circuit to high please can any one help oh i better say what the problem is ok when first start everything fine put you foot down in first gear still fine everything kicks in CHANGE to 2nd gear it starts to hi-cup put your foot down and the turbo starts to kick in then drops out ( take your foot of accelerator quickly aqnd then drop the turbo will kick back in but then drops out in out again i have the same under normal driving without using the turbo its like i wont maintain a steady rhythm please help as am losing faith in peugoet altogether