leaking exhaust how will it effect oxygen sensor??

[Dan Neuman <dneuman@quark.sfsu.edu>]

Hello All,
        So I can't decide how a leak in the exhaust will effect the reading
on the oxygen sensor.  The leak is in the flex pipe before the sensor.  The 
sensor 'measures' the amount of oxygen in the exhaust gasses.. so will a leak
before the sensor make it read lean..too much oxygen or rich, not enough 
oxygen??
        Right now at idle the meter reads really lean then when driving it
reads really rich-almost as rich as the meter can register.
                Daniel 69 2000
                SF CA