What kind of diagnostic tools do you have? Any that will display the wave form of the O2 sensors signals?
https://986forum.com/forums/boxster-general-discussions/77357-p0430-what-do-post626811.html#post626811 had the same problem and there is a discussion there on what he was checking including the wave forms he was seeing.
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Prior '70 914, '99 986 Boxster, '01 Boxster S
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