Engine idles rough, but no significant loss of power during driving (though there is some hesitation accelerating).
All 4 HO2 sensors read very low voltages, never more than 0.2V and pretty steady (no oscillation). There are two banks (one for each side of the V6 motor), one upstream of cat and the other one downstream.
There is noticeable exhaust odor near the front of the car, one mechanic sugested that the front exhaust manifold leaks another pointed at two flexible pipes (under the car). Before I put a couple of thousands in exhaust parts I am trying to understand how is it that these readings can be so low on both banks.