Sounds like a plugged EGR valve and the port on the intake manifold that the EGR bolts to.
I did mine last fall, and it I think it might be possible to clear the intake manifold port without taking it off the intake manifold as follows:
* Remove the EGR valve assembly from the intake manifold
* Check for a plugged valve at the mounting flange and clean.
If it's plugged then the intake manifold port is plugged too,
It may be possible to remove the throttle body and clear the plug via the
opening where the throttle body was removed? Maybe this is a good excuse to
get the $90 boroscope at Harbor Freight and poke that plugged port from the inside?

I'm also told that the plugged ports are a problem from running ordinary dino oil and that things shouldn't plug up so bad if you switch to synthetic oil.

Good luck, Bill