I am in the UK and was speaking to a MB tech today about the egr valve , basically his comment was disconnect it they are a waste of time!!! and cause more problems than they are suppose to sort. (and anway they rarely work properly if at all)
A friends 93 300d had problems starting, after many hours (including tank out because we thought bad fuel) the second the egr valve was disconnected it started? The state of the inlet manifold after it was amazing, full of tarry substance reducing the diameter by at least 50% I cant see that being an advantage.
I believe they were put on in the first instance in cars for the American market. They claim to reduce the burn temperature and reduce the Nox emmissions
With it disconnected my mates car was quicker and more economical, which follows, that it is also more efficient so emissions are lower?
Mine does not have one