You can ignore the O2 sensor as its not a factor at idle (only used during part throttle, off boost cruise by stock ECU)
Sounds like either the TPS isn't giving a consistent IDL signal or the re-capped ECU may have another dodgy capacitor or have damage to one of the tracks on the PCB...I'd start with TPS as its easier, check adjustment, IDL signal etc fist, then have a close look at the ECU...
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