I have a 2006 with 113K on the odometer. I have had this happen 3 times and cant figure what keeps making it happen. Three times now while sitting at a light within the first 10 minutes of start up, a chunk of carbon gets stuck in the EGR valve holding it open and causing the engine to go into a limp, heavy smoke and wont accelerate and throws the CEL. I have made it home each time at like 5 MPH and then popped the valve out and removed the chunk and then everything is great. I clear the code and go on with life. My question is what keps causing it and why does it find the valve only at idle? I have now put the necessary 8mm socket and lady slipper so I can clean it in the closest parking lot.
By the way I use ford fuel additive and the exhaust is 4" turbo back. Nothing in the EGR housing, no coolant that is, and the soot is not really what I consider excessive. Just these darn chunks that seem to find the EGR valve. And it has happened both pre and post 4" Turbo back installation.

Thanks for any feedback.