Will have a look on peugeot autologic tomorrow and see if egr has to be learned, i know on alot of cars now the ecm has to learn the closed position of the egr.

Maybe if the ecm doesnt see enough air mass reading because of a open egr it will affect how it runs ??
I know on the later vauxhall diesels if you dont have the air mass connected into the trunking to the inlet they wont start or rather they start then cut out straight away , found this out just doing routine air filter changes .