Hi, I have a 1995 Isuzu Trooper also. It is a 3.2 Liter Engine. I had the same
problem. I pulled the codes when the check engine light came on and it said
Fault Code 44 which is an OS2 sensor. It is located just in front of the
Catalytic Converter, just replace it, this will also increase you gas milage. It
costs about $75 at Auto Zone.