Toyota Repair: I need help on my 93 Previa van, o2 sensor, rich mixture

Question
I have a '93 previa and it stalls when driving. The diognostics says fuel is too rich. Do I have to change the O2 sensores? Front? Back? Or the fuel filter? I went to Schucks and they told me to go online so hopefully you can help me.

Answer
It would help if I had the code number but it's probably #25/26, this can be caused by an engine misfire condition and may not be a problem with the O2 sensor, the O2 sensor is reacting to a rich mixture condition which will turn the check engine light on, this condition could be caused by a misfire. It could also be caused by an internal combustion leak such as a blown headgasket so I would recommend finding the cause for the rich running condition, replacing the O2 sensor will probably not fix the problem.