The egr is located on the exhaust manifold. The small vac line attached to it comes from a switch-over valve under the front plastic cover if front of engine.
The ecu sends an electical sig to the sw/ov which opens the valve to engine vac. This in turn pulls the diaphram on the egr , opening it and allowing some of the exhaust gas to recirculate back to the intake manifold, cutting emissions.
The ecu will not send this sig at idle or wot, or until the engine is warm. . [ there are other paremeters for the ecu sig timing, but this is the basics]
So, if you hand pull about 12" of vac on the egr at idle with a warm engine, you are creating a very lean condition [ vac leak] and the engine will attemp to stall. [ run very rough]. This indicates that the egr is opening. Now, release the hand vac and the egr should snap shut. Engine should smooth out. But sometimes the egr sticks open, thus the diagnoses of "Running rough at idle when engine warms up".
There are 2 other test for this situation that I like to do while I am there. One possible is that the diaphram in the egr itself
may leak by and cause an internal leak. The test for this is to see if the hand vac will hold the egr open for a period.
The other [ athough remote] is that the sw/ov has a little vent on it that lets air back into the vac line when the ecu stops the sig to the valve. What this vent does is it lets the line between the egr and sw/ov lose its vac to the outside air and return the
egr to the closed posistion. [ in other words, it is possible for
the trapped vac in the line to keep lifting pressue on the egr diaphram].
A vac gauge somewhere on the intake side of the engine makes verifying these test a little easier.
So, this may/may not be your problem, but it shoud be checked
as it will cause this type of prob. and is easy enough to do....
As an added PS to this test,:
This is also a good test to do on the infamous egr intake tube
blockage at the intake side of the engine on the 104 engines.
There have been many post about it and this test will help diagnose that problem as the tube fitting at the head is just about impossible to get to..