http://isuzufaq.ibctech.ca/#faq1
You need to clean a little more then the EGR. you also need to clean the egr tube too.
typically it take a half of a can of carb cleaner (1-3 bucks).
your dealer charges 495? I would ask them for a break down of what they will do for the money.
My dealer charges 100 bucks for it (I can do it myself in under 30 minutes).