1995 GA SE, 3.1 EGR Problem

I have had this problem for about two years, when I'm on the highway if I suddenly drop speed from 70 to about 40mph I get a SES light. I brought it to a shop to tell me what was wrong and they read the diag. codes and told me the EGR valve itself was bad. They wanted to charge me $600 and to fix my directional switch, I went to my local auto part store and paid $200 for it instead. I installed it and problem still exist, I later on changed the oxygen sensor and still had no effect. Today I had trouble starting my car (turned on, but very weak, turn off a couple of times, felt like fuel problems) and the SES turned on about 1 min after I turn on the car, the rest of the day it keeped on doing this. Can this be that the passage to the valve is clogged up badly or can this be something else. Once in a while I hear a rattling noise while going up a hill when I'm at 40mph, my in law thinks it could be that my timing is off. I don't know how to clean the passage and no one around me deals with this problem, I'm kinda worried about the car, because I've read this can help kill headgaskets, and I've been down that route before on my last GA. I haven't changed the fuel filter since I got this car two years ago, I plan on getting it changed but I don't know if it would give me a SES warning. Please let me know what could be wrong.


Thanks for your help in advance

The EGR passage cloging is a common problem on those engines.
There are 2 ways to clean the passage..first involves removing the plenum and having it "bead blasted" to remove the deposits or the second way is to spend the afternoon picking the deposits out yourself.

On the SES light, you will need to retrieve the codes to do a proper diagnosis.