lumpy idle at 900rpm

Yes, you can do it, but it will probably generate a fault code in the Engine Ecu and if the EGR valve is not leak free (by pass inside) it will not very helpfull because you will figure the valve is close because it disconnected but if it by passing your test will not good. . . .
If you want to do a test i suggest to you:
Warm-up the engine, up to be able to duplicate the problem,disconnect the egr pipe come from the egr cooler at the egr mixer on the LH of the engine (just above the electrical pre-heater if equipped, run the engine in this way standstill, check if you are able to duplicate the problem again?
Let me know
Ben

 

Yes, you have the right one.
Ben

 

Run the engine with the egr pipe disconnnect open (only standstill).
Depends of you egr pipe style it can be easy or more difficult. . .
One pipe model have a long flexible hose with v band clamp over the valve cover (easy) the other model have a short orange color hose (most of the time that hose come paste to the pipe and need to be split to be able to remove it, you need a new one for reassembly.
Ben

 

Good, at least we know it's not come from the EGR circuit.
Yesterday you told me you have to replaced the egr cooler because you have a big coolant consumption (1 Gallon per day) i'm not sure but due of the lot of coolant in the combustion chamber the engine may be did a Hydraulic lock and bent a connecting rod ?
Recently i saw this problem in a D-13 after a drop valve situation on cylinder no 2, the liner no 2 crack and the coolant flow back in the intake manifold and the piston number six at TDC position was .025 (thousand of inch) lower than the five others due of a bent connecting rod .
When the dealer ran a compression test and the balance with the PTT tool test did you saw the result ?
Ben

 

Another question did your engine ran more regen than before ? (Before the vibration starts )
Ben