Chevrolet Repair: 1994 Suburban EGR valve, transducer system, egr valve

Question
The EGR valve opens at about 1500rpm. It doeswn't matter if the engine is loaded or in nuetral. It then stays open until the engine chuggs down so much there isn't enough vacuum to pull the valve in, when the engine stabalizes again, the valve is reopened. The valve has been replaced along with the control solenoid, the MAP sensor,  the TPS, and finally the ECM. The condition still persists. The sol. is being commanded on at the above mention RPM. This was determeined by the signal at the sol., not the output of the ECM. I am leaning toward a wire getting grounded out.(I suppose it is possible that the driver in the "new" ECM is bad showing the same symptoms as the previous one, buty that seems unlikely.) Any tips or guidance you have would be greatly appreciated.  

Answer
Hi Keith,
A grounded wire would probably stay grounded, which would keep it energized all the time I believe.
There are a couple EGR systems, and I don't know which yours has.
But if it has a backpressure transducer system, it uses vacuum, but also uses exhaust system backpressure.
If you have a restricted exhaust system, that could be generating the backpressure.
That chugging down till it stabilizes....any chance it is chugging down due to a restriction?

Van