Hyundai ix35 1.7 CRDI P0404 Error

Hello everyone! I have a problem with my Hyundai ix35 1.7CRDI built in 2012. I have the error code P0404 Exhaust gas recirculation control circuit range/function in the fault memory. On recommendation of my mechanic the AGR valve has been renewed, the error can be deleted and after starting the engine it runs also without problems, as soon as you drive up to about 2000u/min it stutters strongly, takes gas away and it feels as if it runs out any moment. Hlag for me? I thank you already