Got my truck to the ford dealer for a diagnostic for the CEL (codes P1335, p0404) popping up. They said that the EGR valve (which was just replaced again) was stuck wide open. They said the cause is a ton of carbon build up. They do not do the cleaning of the EGR system and said that they don't know of anyone that does. They said that the intake would have to be taken off and hot dipped. Is there anything I can do on my own, any fuel/oil additives I can use to help clear it up any?