94 Camaro digital EGR problems

94 camaro Digital EGR valve 3.4 SFI automatic Service engine light comes on going down the highway when I let off the gas. 3 codes for all three EGR solenoids.
I have pulled the EGR valve off cleaned and tested it with 12 Volts, all three solenoids work. Removed the EGR tube and cleaned it, replaced it with new gaskets, made sure hole to the valve is open. Sprayed the tube with WD40 while the engine was running, no change in the idle (no leaks). With the key on and a wire from the 12 V on the EGR harness and shorting each solenoid to ground works fine. With the engine running and shorting each solenoid there is no difference in the idle of the engine.
Could there be a blockage in the exhaust manifold? Could there be a blockage in the intake manifold or a sensor that detects whether the EGR opened or not? Car runs fine, just tired of seeing the service engine light coming on. I know how too disconnect the service engine light, but thats like taking the battery out of the smoke detector. Any leads on what else to check, would be much appreciated. Thanks
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Mike wrote:

That sure sounds like a blockage. And for the most part, a blockage is what turns on the code. The ECM will under certain conditions open the EGR valve and if the engine doesn't kick, it figures the valve is not working.
--
Cy Welch
89 Camaro RS 5.0 TBI
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