Hello, According to me, this is the pressure Regulator on the pump (DRV) me ? happened to you personally the most? times on the pi? cars equipped with a pressure regulator bosch, pu? happen that because of diesel polluted is plugged the microfilter on the tip of the regulator just to take it apart and clean it, as you know, you will damage the matching rubber or and lose pressure, or that it is faulty.. replace it and go quiet, if it was the EGR valve, there would have been pressure changes in cos? obvious then you just unplug the Egr valve itself to discriminate the problem