Mitsubishi Diamante 3.0 P0400 Fault: EGR Control Solenoid Valve Diagnosis and Testing

I'm currently experiencing a P0400 diagnostic trouble code on my Mitsubishi Diamante 3.0 engine. After testing the vacuum line and manifold EGR valve port, both appear to be functioning properly. I suspect the issue lies with the EGR Control Solenoid Valve. During my test, the inlet vacuum at the solenoid was measured between 5 to 7 Hg. When I disconnected the electrical connector and blew air into one end of the solenoid, air flowed freely through the other end—indicating no resistance. Upon applying power to the solenoid, I heard a distinct click, followed by free airflow when blowing from the same port. This behavior suggests that the solenoid is not maintaining a proper seal under electrical activation. Since I replaced the EGR Control Solenoid Valve a year ago, I'm wondering if this could be a recurring issue or whether the current symptoms point to a faulty component despite the previous replacement. Any insights on how to properly diagnose or verify the solenoid's functionality would be greatly appreciated.