Hi guys,need some help with this one? Recently my 2009 dispatch Relay 120 lwb 2.2 Threw a code for failed egr. This was replaced with a brand new unit and the eml was reset by the garage. 2 weeks later the eml came back on with this code p1304 (egr calibration high? The van runs fine apart from a hesitation between 1.5 and 2.5 revs with light on. If I reset ECU then start the van the light stays out and the engine revs correctly but once I turn her off,the code returns with the same hesitation and what I feel is slight detonation. Any thought would be greatly received as I'm stumped. Thankyou