check engine light & fuzzy computer pictures

[Joan Kotjarapoglus <jkot+@pitt.edu>]

I am purchasing a 92 100 which is in excellent condition and at a very
good price from a dealer acquaintance.  I spoke with the owner and
reportedly the only problems with the car is a fuzzy computer pictures on
start up and the check engine light comes on after about 50 miles of
driving.  His mechanic tells him there are 2 oxygen sensors, each of
which is very expensive and he does not know which one is bad.  Any
suggestion on which if any to replace and parts source.  Also, is there
an easy fix to the fuzzy computer pictures on the instrument cluster on
startup.?  George K   jkot@pitt.edu