Hi

Had one of thesewith exactly the same problem. Very confusing because the fault code is reporting a rich mixture when the fuel trims are obviously lean!

You have sorted the most common lean problem with these by changing the piping under the inlet manifold. I must confess, aftermarket o2 sensors are not best for these,with the front one being broad band. I have seen them fail quite quickly.

The problem our one was drawing air in through the rocker cover gasket and the oil cap. The Smoke Pro did not show this up.

Worth a look.

Simon