Leon Speed

... right behind the cats cause:
a) lower fuel economy
b) higher idle
c) both, or
d) none of those, just more noise

Ducman82

loss of back pressure, but i cant see it causing anything more that noise.

The Forgotten On

Just noise, all of the other choices are caused by vacuum leaks and marginally affected by a bad O2 sensor.
Since it is from behind the cats it couldn't affect the Lambda unit as the O2 sensor is in front of the cat.

Leon Speed

I was thinking since the cats aren't that long there might be chance of O2 "interference" from the leak. No? Too far fetched? I guess I will start looking for a vacuum leak.