at idle it is turned OFF [ zero vacuum to the valve ], and its vacuum source is usually such that a restricted orifice effectively puts it [EGR] in a different pressure zone than the tranny shift control system. Hmmmm... tell me the Year and model and I'll get the Engine Vacuum Diagram. In any event, assuming you have an automatic tranny the EGR vacuum source should be isolated from the tranny shift system... also the EGR opening should be minimal to none at full throttle... so after you start pressing the accelerator, the switch on the valve cover opens the EGR full and it should then start closing as you approach full throttle. If in doubt and as a test, I would put a golf "T" in the EGR line blocking it off so it does not operate at all [ except if it leaks exhaust into the intake manifold]... do this to see if the car runs better than when the EGR circuit is hooked up. IF it runs better when the EGR is disabled, then you should check to see what your State regulations/rules are and then make a decision as to whether to take a chance on leaving the EGR disconnected. Many, many, many of these early EGR's [1980 was the first years here in CA] are disconnected because they make the engine run so poorly with black smoke and a loss of fuel mileage.

Let me know: YEAR & Model, and whether auto or manual shift?
If auto, how is the tranny shifting?
Maybe I can and give you some further help with engine vacuum system.
If you are so inclined to get into this IMPORTANT issue of vacuum control systems, you should invest in a hand vacuum pump that will cost you $40-$60... but having one is essential to such DIY work projects.

Best regards,
Sam