80q running rich at idle

[Blu]

I can smell that my engine is running rich at idle , does anyone have a
checklist of items that could be responsible for this?

FYI --my cat went bad which leads me to believe something is definitely
wrong. The car starts pretty well and there is just the slightest roughness
in its idle. Would having a bad cat have anything to do with the car running
rich (or at least smelling like it running rich)? would a bad cat "throw
off" the o2 sensor?

Thanks
Blu
'88 80q