It doesn't work.
Really, rough running if it's open too much and pinging and worse gas milage if it's not opening. But EGR valves don't die too often any more. Usually the passages behind the throttle body get clogged. It could also be the DPFE or solenoid or even hoses. Best way to start checking is to get some small tubing and while it's idling pull the vacuum line off of the EGR valve and put you tubing on it and suck. If nothing happens, the passages are probably clogged. If the engine almost dies, the passages and valve are OK. If you want to dig deeper, you will need a vacuum guage and maybe a meter.
FYI - if the car has 60k on it, the EGR passages should be cleaned and every 30k after that.
