I have a TPI 1991. I have two nb o2 sensors
one on the right side and one on the left side in
the header pipe and they are in the same place
on both sides.
What would cause the right
side to run alot richer than the left side at idle.
The left side does not register at idle, but
does when I get on it and it reads
the same as the right side.

 

I only have one o2 sensor on both my '91's.
Never seen one with 2.

 

You are right this is not stock this
was added to the header pipe
one both sides