I hate EGR with a passion. Its put there to reduce emissions, specifically NOx, by reducing the peak combustion temperature: but this reduces engine efficiency, increasing fuel consumption also increasing hydrocarbon emissions.
It's particularly vile in diesel engines (note the avatar
) where it causes choking of the inlet manifold with carbonised oil sludge and also is responsible for most of the smoke emitted by modern diesels: yes, the emission-control measures for NOx specified by California and so imposed on the whole world cause increased emissions of hydrocarbons and smoke particles, which California also regulates.
Water injection would be a much better way to control NOx, having the additional benefits of improving engine efficiency, but you'd have to remember to fill the water tank every so often, and the average Californian has trouble remembering which way is up.
The environmental studies that lead to legislation against NOx emissions from vehicles are deeply flawed, and there is a strong suspicion that the legislation is driven by oil companies who prefer engines inefficient and dislike diesels altogether.
It's possible your EGR valve has started to stick from deposits of carbon, so it might just need a clean, especially if you do mostly short journeys or relatively little open road motoring.