You checked the diaphram in the EGR valve & it appeared to be good - except for the Engine on test. This tells me that the EGR passages to the TB are all plugged up. Clean those beasties out!!
Once done, be sure both hoses & the electrical connection to the DPFE are secure and start the car. It may be all you need. If the engine is still hunting for idle, clean the Idle Air Control valve.
Those two things should set things right, you don't have to purchase anything except a $4 gasket & some cleaner. Even if the DPFE has gone belly up, the idle should not be affected that radically. I had to replace mine after a TB cleaning to rid myself of a dreaded CEL & my car never even ran poorly.
Give them a try, you have next to nothing to lose (assuming you do it yourself).
