P0430 code

I recently tuned up my � 04 Escape. New plugs and coils, a new PCV valve, new intake manifold gaskets, new fuel filter, new air filter, and I cleaned the mass air flow sensor. Along the way, I verified that all hoses and connections were good and there were no vacuum leaks. After all the work, the engine ran smooth, idle was perfect, acceleration was crisp, plenty of power. Now, a week and a half later, the engine light is on and I get the P0430 code, which states "the front catalyst efficiency is below threshold.” The Escape still runs perfect, the way it did after the tune-up. So that is making me believe that the issue is an O2 sensor, NOT the front converter. If that converter was plugged or damaged at all, wouldn’t there be a decrease in performance, even a slight difference? Like I said, the engine still runs perfect. Any advice on diagnosing the issue, or what the cause could be? Thank you.

Merlin, thank you. No, I do not hear any rattles, nothing at all. I was thinking about having a diagnostic test done while the vehicle is running. Would that pinpoint if a sensor is bad, or would the tailpipe emissions test be better? I do know the converter is very expensive, so I really hope that is ok. IF, that converter is damaged, would I risk more damage to other components, the rear cat fro example, if I let it go for a while? For money reasons, if I can wait to replace the converter, that would help. Thanks again merlin.