what is the egr and what does it do?

Would the egr valve have anything to do with poor performance with my 91 lummy z34?. What happens is it idles rough sometimes at the light and when i go to accelerate it stalls sometimes. It just had a tune up but still my check engine light is on.

It could cause a rough idle and stalling. They are known to get carboned up and not fully close. The EGR recirculates exhaust gases into the intake air to reduce combustion temps thus lowering the levels of NOx(oxides of nitrogen).

Find out why your light is on, the procedure is posted in a few of these forums.