Thanks for the responses. To elaborate a bit more, I offer the following. I don’t have a longstanding relationship with this mechanic, as we just moved to the area and only have been there a few times for oil changes, etc. When the car was taken in, there were no codes found. However, since that time a code of P0406 would show up one time, then be gone the next. It has not shown up again in the last week. According to this mechanic, he believes that the carbon buildup can sometimes make the egr valve stick and could cause this code to appear. As I mentioned, this code is no longer showing up now. Regarding how he knows there’s carbon buildup, I guess I can’t be totally sure. He explained it to me at the time but not being an expert, I didn’t understand all of it. He had indicated that when they removed the MAP sensor, etc there seemed to be a buildup in some of the lines? In any case, it sounds like I should maybe take it to another mechanic for a second opinion or to a dealership? I’m currently not driving this vehicle much and will take awhile to run a couple of tanks of gas through the car and I’m anxious to get a more certain diagnosis.