I have posted multiple times about a running rich problem w/ my 91 740 wagon, B230FT. Error codes 232, 113, essentially rich.

I checked everything & nothing really stuck as a fix. I guessed I had an exhaust leak I couldn't see of hear causing the O2 sensor to falsely see a weak mixture & compensating rich. I followed a helpful poster's (sorry couldn't find who)advice & reversed my shopvac & blew into the tailpipe pressurizing the exhaust. I disconnected the turbo hoses & sealed the openings w/ rubber gloves. I sprayed soapy water over the exhaust manifold, turbo etc.
I found very tiny leaks on the exhaust manifold but the kicker was a good deal of bubbling from my O2 sensor body. It was a generic from a V8 5.0 litre Mustang. The leak was in the body just below the sensor head. I changed this & 3 days & a couple of hundred kilometres & no error codes. Yes the O2 sensor passed all the green book tests & a couple of helpful ones from Lucid.
Put it in the memory banks people it hopefully saves you some time.

ibs740