Cross counts

[Geoff & Sue Richards]

Hi all
Today was checkin out engine check light comin' on
in Holden 3.8 v6 and Tech 1 showed DTC relating to 
02 sensor. By accessing data list 02 was readin' 900mv
at idle indicating rich mixture at times reading was goin
above 1000mv,while this was happening I removed fuel
pressure reg vac hose to create vac leak and see reading drop
but instead it increased slightly
Could this increase be the result of high FP due to reg hose off?
Checking 02 cross counts at steady 2000 rpm showed none
indicating slow sensor?
Your thoughts please
After fitment of new sensor data was rechecked and cross counts were
still low although better,I was expecting around 10-12?
Sensor did start reacting better on road than in shop
Could this be the result of stale reference air while sitting still?
Thanks
Geoff