If the 02 sensor reacted instantly then I would doubt your problem is with the sensor.

Has this definitely got a map sensor and not a air flow meter as I thoght the xe1 used afm and the xe used map.

I think its probably in need of smoke test to see if its got any air leaks, in the past I've had egr valve body's leak and exhaust manifold crack which may open up with heat as the engine warms up.

Remove heat shield to have a look.