Hi All, I give up

Is there a EGR valve in my 300E?? I can't find it but parts sources suggest that it does have one. On my exhaust manifold I do see a flat spot where in later models the EGR mounts .... but nothing there on mine.

cheers, guenter

ps I'm trying to address a stumbling/rough idle (500rpm) after engine has warmed up. When cold it idles nicely actually around 900 rpm. It's driving me nuts trying to find the cause....