Rough Idle, Check Engine Light, Wacky Tach, EGR Valve?

Well, after many many years of not driving my Mustang and not visiting the forum, I'm back.

I have a 1991 2.3L Mustang LX. It has ~97K miles on it.

Recently I have noticed that my tach is going insane. While idling and/or driving it jumps all around: 500 -> 3000. There isn't a pattern, it just happens all the time.

I've also noticed that my Check Engine light is on a lot. I took it to Autozone and had them 'run the codes'. They said since I have a '91 that it the machine isn't as accurate, but they said they were pretty sure it had to do with my EGR.

So I searched around on the stangnet forums and read about people having sort-of-similar-but-not-the-same problems. People have said good things about blocking the EGR *or* cleaning it with carb. cleaner.

My question is -- Where the hell is the EGR? I've tried to find pictures or diagrams or anything to help indicate its location. I'm stumped. I'd like to try cleaning it to clear up my problem. So if anyone could give me a picture and/or instructions on where to find it, I'd appreciate it.

OR if anyone has any better ideas on what my problem could be (I'm not very confident in the autozone people) I'd appreciate advice.

Thanks for reading.

-Dustin