egr valve isn't opening.what would cause this issue. on 1993 Ford F-150 Lightning

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i just went to my local repair shop to see if the check engine light thats on is still reads the egr does.the scan machine he used said egr isn't opening.what would cause this to happen.he also pulled the vaccum line off egr to see how much suction was he said there wasn't idles a little unsteady.but it i drives without any issues.if valve wasn't opening wouldn't truck be running alot worse then it does.i mean idle wise.
(1) Answer
The EGR Valve will only have vacuum to the valve under certain circumstances, and never at idle. EGR systems can have carbon deposits accumulate in them and clog up, and this might be what is happening. If the valve was open at idle you would have a rough idle, but you probably wouldn't notice it otherwise.