problems after replacing EGR

I have a 94 Thunderbird 3.8 LX. Last week my check engine light came on and stayed on. Took it to a shop and had the codes read. As a result, I had the EGR sensor and EGR contol replaced plus a new hose, that's what was on the receipt. After getting my car back, I have noticed that the car has a rough idle upon startup. The rpm starts out at 1500. Then after 5-10 seconds, it goes down to just under 1000. I then put the car in reverse, or drive, and the rpms drop further to 600 and will jump around between 200 and 800. It sounds as though it wants to die but hasn't fully cut off yet. The voltage gauge also fluctuates at the same time. After driving for about 10 mins this problem doesn't occur when I'm stopped at a traffic light. The check engine light does not come on either. Is this a result of getting new or "clean" EGR parts or is this something unrelated?

Curious, wonder if your EGR valve is stuck open...