The story continues, hopefully with a happy ending. On the fourth trip to the dealer the tech's theory was that a small piece of carbon was still loose in the system. He has 20 years experience in emissions and he was frustrated too. He cleaned everything again and asked if he could keep the car overnight and drive it home and on a long test drive. He drove it 172 miles and no returning light. I am now at 500 miles with no light. The dealer, Russel Subaru, has been great here. There was only the initial charge to replace the EGR and back pressure valves, plus they gave me a free loaner, a 2003 Baja, while they kept my car. Dealers get a bad rap many times but I highly recommend Russel to anyone in Maryland. These emissions codes can be tricky but they worked with me to get it fixed.