How about the front O2 sensor?
I cleaned the TB out before my wife took the Baja on a trip but it was a simple spraying the butterfly and the port leading up to the idle valve. After 500 miles it is still doing the same. She is still on her trip so I won't be able to really dig in to it
But the "only when the air conditioner is on" is a little confusing. It doesn't following the compressor turning on/off.