Going back to the original question posed by Carl, I agree with your comments and that was part of my first post on this thread. Mark's response to my post was
"Historically we do not throttle a diesel,we mealy control the speed of the engine by the amount of fuel injected, so if what you say is correct, then how did we overcome this "problem" you have highlighted before EGR came about? "
This got me thinking in a totally different light about diesel AFR's. I may have taken Mark's comments too literally but I think he was trying to say that there is very little control over a diesel AFR. He is of course quite correct in what he has said, and although I have learnt something about the subject I still think my original description on the purpose of EGR was fairly accurate. Funny thing is that since the start of this thread I have had two Astra's come back (different egines but same part No') with EGR Position Sensor faults. Both of these cars have had EGR's replaced about 18 months ago and both have had regular servicing and used under normal conditions. Neither of these however, looked anything like the ones in Carl's pictures.
Regards, Bryan.