I drive a 2003 Volkswagen Jetta with a 1.9 liter turbo-diesel engine. I often get well over 50mpg on the high way, and I love the fact that I have such a fuel-efficient car that is also fun to drive.
A few months ago, my check-engine light came on, and my local mechanic told me the EGR was bad. He suggested I could remove it (which I did). I did a bit of research on the issue, primarily concerned with the environmental impact of removing the EGR. I came to the conclusion that I wasn't really sure, but that the environmental pros and cons were nearly a wash.
Of course, the EGR is mandated by U.S. emissions standards, with the purpose of reducing NOx emissions. Although I have read claims that this is likely a misguided effort. Also, the addition of an EGR also increases other emissions. If my rusty memory serves, removing the EGR allows for more complete combustion, resulting in lower particulate emissions... And less restrictive airflow also improves engine performance slightly (by up to 2HP at high RPM for this engine, if memory serves).
And lastly, the removal of the EGR means I never have to clean the soot out of my intake manifolds again, which means fewer chemical cleaners, and less maintenance cost over the lifetime of my vehicle. And no EGR means the EGR can't break and need to be replaced again.
So all things considered, and legalities aside, is an EGR (specifically in a 2003 VW TDI engine) an environmental gain or loss?