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It is the EGR control solenoid. The EGR (Exhaust Gas Recycle) valve. The EGR is controlled by the ECM and allows exhaust to enter the intake manifold to aid in cooling the combustion process, supposedly lowering NOx emissions.
I have my valve blocked and disconnected. The EGR valve is the round thing next to the solenoid.
If your state requires emission inspections you may have to get it repaired.