My ZD30 developed this fault without any warning, I took of from traffic lights and it would not go over 2000 RPM, holding full throttle it ran like it only had 2 cylinders, back off and hold under 2000 RPM and it runs normally. I managed to creep home and while I was sitting in the driveway I tried full throttle again. After a couple of small surges it suddenly went to full RPM, revved up and down normally. I thought that it had cleared itself. Had a coffee and came back to move it and the fault was back and won't go away. I checked the fuel filter, clean as. Changed the filter anyway, no change. No knocks or rattles, just feels like there is a governor limiting RPM to 2000. Could the EGR cause this??