Not my job fortunatly, but I have just had a customer who is a perfectly competant DIY mechanic (Rebuilds old Porches) who attempted to remove and clean/replace the EGR valve on one of these.

After which the engine coughed and refused to start. Sounding like broken cambelt.

It would appear that removing the EGR dislodged carbon deposits which subsiquently dropped down into the engine and jammed the valves open far enough to be hit by the pistons!

The carbon deposits so far recovererd are not the soft squishy stuff normally found, they are like little rocks! It occurs to me that tthe only safe way of removing an EGR on one of these (and possibly on many other vehicles too) might be to remove the manifold first and only dismantle it away from the engine...

Unless anybody has a better idea?