Thread seems to be getting interesting from what I gather from everything I have read and seen in my short time so far is that on a diesel engine the vacuum in the inlet manifold must be very minor (will be having a look tommorow at an actual figure) due to the fact the only thing causing it is the piston going down on a intake stroke and obviously on tick over the excess air in the manifold is not always required so to answer your question Keith if you restrict air intake you could reduce the amount of air going in so maybe there would not be excess air to worry about so no egr required but obviously it is not as simple as that or the vm would have it in place? Just read some interesting info on egr about using an egr system actually creates particulate matter which is mainly carbon so due to regulation is why we now have to have particulate filters which I also seem to see alot of blockages so it all seems a bit one step forward then one back
thanks