I had all the problems mentioned here. Loss of power, black smoke etc, on my avensis D4D. I cleaned the EGR valve and it was ok for a short time and then the problems returned. I read that it was possible to blank off the EGR valve and take it out of action. I made a plate and fitted it behind the EGR valve and refitted it. The electrical system still thinks it's working and therefore no fault codes or lights. The problems have gone, the power has returned, and the fuel economy is miles better. Just blank it, it's no use to anyone.
Mick Wray Denmark., December 2013