Exhaust leak affecting O2 sensor?

[radek at istar.ca]

Hello group.
I discovered an exhaust leak between the manifold and the catalytic coverter - looks like
a blown gasket.  The leak is BEFORE the exhaust gases reach
the O2 sensor.  Would this affect the sensor's readings?  The car does not idle properly
and sometimes gives me the "check engine" light when driving.
Could the leak be the cause? TIA.

Radek
'88 90Q
'93 VW
Eurovan

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