1988 GMC k-1500 5.7L EGR valve stays open during idle

Whenever I start my truck it idles erratically meaning it would idle really fast then slow down. The kind of truck I have is a 1988 GMC k-1500 1/2 ton 4x4. It has 168,000 miles on it. I know it is the EGR valve staying open during idle. I have not been able to find out what is causing it to stay open because there is something telling it to. I have brought it to places and they told me to replace certain parts. I had replaced the EGR valve, the EGR valve solenoid, ECM, replaced all of the vacuum hoses and even cleaned out the combustion chambers which they were not even dirty. Everytime I have the truck running, you know the valve is open during idle because it will sound like it will stall and then it will try to catch itself and try to go back to normal. I had to unplug the EGR valve solenoid electrical part since there is something telling it to stay open during idle. When I have it plugged in, it stays open all the time, sounds like it is going to stall, and even is hard to brake when the valve is open. Since the braking was almost impossible with the valve open that is why I had to unplug the electrical to the EGR valve solenoid. I had replaced tons of parts and still have the problem and no garage has been able to figure it out and they all told me to unplug the electrical part to the EGR valve solenoid so that it doesn't stay open all the time until I can find out what is causing it to stay open. I would like it to be fixed and not have to worry about my Miles per gallon decreasing, truck stalling and not idling correctly because the EGR valve is not function right. I can't find anyone who has had that problem nor can I find what is causing it. I have had different people tell me that it is a part that has gone bad or that it was something else causing it and I have decided to go for professional help. I would love to know if anyone have had that problem before or if they know what is causing it. It would be great to find out what the problem is.