here you go
You need to put negative pressure on the vacuum port of the EGR valve and then try to blow into one of the other ports - if air comes out the other side then the EGR valve is working. If the valve is working then you want to check for pluggage in the EGR pipe from the valve to the intake manifold.
With the engine warm - at operating temp - put your vacuum pump on the vacuum port of the EGR valve and put some negative pressure on it. The engine should lower in idle speed and/or near about stall. If this does NOT happen then you need to "rod" out the EGR pipe from the EGR valve to the intake manifold. You will need a piece of old speedometer cable that is flexible all the way to the end. You may have to modify the speedo cable because most of them have a rigid end that will not make the 90 degree bend through the EGR pipe at the intake manifold (you do not need to ask me how I know this). Anyway, shove the speedo cable through the EGR pipe, hook a drill motor to it and spin it inside the pipe. I found that the last 1 to 2 inches of the pipe at the intake manifold was where the most severe pluggage was.
'85 300D, no check engine light here