Do a simple EGR test.
The egr gets no vac. from the ecu until closed loop [ warm 02 sensor]. So , once it opens , it may leak/stick open. This will show as a large vac leak at idle. The ecu also calls for no egr at idle, but if it has opened and sticks open, rough idle will result.
The test is to pull a vac on the egr valve line with a hand vac pump at idle . [ or steal vac somewhere off engine for test.]
At idle , when you pull the valve open, the engine should run pretty rough. When you release it, you should hear it pop closed and eng idle smooth. If it sticks open, you have found the problem. If, when you give it vac., it does not hold the vac., it is leaking by internaly , also causing same .. If so, replace it.
It is common on vac leaks to not be as pronounced with a cold engine as they are running rich til warm and that helps off-set the added intake of air caused by the leak.
Worth a try.....