2006 Honda Ridgeline P2279 Code: Rough Idle and Surging in Park - Solutions and Diagnostics

I own a 2006 Honda Ridg- line with 300,000 miles. I'm currently experiencing Diagnostic Trouble Code (DTC) P2279, which is associated with a rough idle that surges occasionally when the vehicle is in park. Previously, this issue was accompanied by misfire codes on all cylinders and rich fuel trim readings for both engine banks. The car would also hesitate during startup. I recently performed a valve adjustment and replaced the intake manifold and valve cover gaskets. After these repairs, the misfire and rich fuel trim codes disappeared, but DTC P2279 has returned along with DTC 0420 for Bank 1 catalytic converter below threshold. I've thoroughly inspected the engine for vacuum leaks using propane, brake cleaner, and water—no obvious leaks were found. The vehicle runs smoothly at highway speeds and shows no stumbles during acceleration. Additionally, I'm experiencing a whining noise from the power steering system. I replaced the pump O-rings, which provided some improvement. While this issue is not directly related to engine performance, I've read that power steering systems can have vacuum connections that may influence idle stability. I'm wondering if there's any known connection between the power steering and idle control. Could the evaporative (EVAP) purge valve be contributing to this problem? Are there other components or sensors I should investigate? Any insights, troubleshooting steps, or recommendations would be greatly appreciated. Thank you in advance for your help.