POST THE CODE # they found. Parts guy telling you "it's EGR" is not enough info.
Here's an easy way to diagnose the egr valve
Find it, pull the vaccum line off of it and plug that vaccum line. Drive it for a few days. Ideally, you should do this when it is NOT stalling and running rough.
If it never does it again, it was the egr valve. Sometimes you can clean the carbon out of them (I've used black powder rifle bore cleaner and a .22 cal. bore brush). When you remove the valve, you'll see that shaft in the middle. Push on the bellows and the shaft will move. When you have it fully extended, plug the nipple with your finger and it SHOULD stay in that position. If it doesn't, replace it. If it DOES, clean it while it's in that position.
Carbon tends to block it from completely CLOSING. In that condition, you will have EGR flow at idle and it'll stall. I've seen them be carboned up so badly it wouldn't idle at all and be very hard to start (wasn't a Ford tho').
You really need to post the code #. If the code is EGR flow excessive, try cleaning the valve.
Oh, and soak that big nut in PB Blaster before you wrench it off. That big nut should be the first thing you loosen to get the valve off.
Don't forget to clean the carbon out of the ports on the intake while the valve is off. It can be so bad that you need to chip it away before hitting it with a solvent (carb cleaner).
Here's some helpful info: http://www.focushacks.com/index.php?modid=80