A big hello to all I am David from the UK , and I have just bought a 2.2 Cdti Honda Accord and boy it packs a bunch. I have also ordered a KWP2000 and I am interested to learn how to get the best out of this engine, and for the experts to maybe do a few mods for me so I can learn from how they do it.

Also I dont understand what EGR is and I assume by looks of it its sensible to get this turned off. What is main reason for this :0)

Welcome and nice engine there.
The EGR valve is the Exhaust Gas Recycling valve. It takes some of the exhaus gases and puts them back in the combustion chamber. This greatly lowers NOx emissions. Most engines (also petrols) now include one or two of these valves.

For obvious reasons it lowers the efficiency of the engine. Of course the engine does not "like" breathing it's own exhaust gases, when on the standard map this does not effect the power greatly as the valve is turned off at higher power requests, but when tuning it is better to turn it off. Also it is a component known to give problems easily and may need cleaning if the engine has done a lot of miles.

Welcome to the forum

Welcome.