That explains a lot... Do you think the egr modulator can go bad? i checked mine and its clean.
They can, but I doubt it.
Without backpressure on the bottom diaphragm, the EGR won't work. You can test for leaks.....
Remove that hose, and plug in a fuel pressure gauge with a long hose so you can monitor the back pressure while driving.
You need to see at least 1/2 psi at the 25mph 2nd gear, steady speed for there to be EGR to lower the NOX.
With my 86, it just fluttered a little until I added my 'special' back pressure gasket and it went to about 1 psi.... (this is how I aced the NOX last smog test)