CEL possible O2 sensor 1.6 bar now 1.3

[SuffolkD at aol.com]

Lister(s): 200 20V 3B

I'm prepping for a track event and seem to be slipping backwards.

We chased down some vacuum leaks and the car ran to 1.6 bar (93) octane.
Now the car has hesitation and when it does, it only pulls 1.2 / 3 
bar.........where I started before chasing vacuum leaks.............

Now the ChkEngLight has come on. and its on quite a bit now. (Today)
Vag-Com car tonight  DTC is :
00537 - Lambda Oxy sensor regulation 08-00 control limit surpassed.
Now I just put this new $130 full cord & plug one (I wanted it) in last Aug.  
~7,000 miles ago.  (Car sat all winter)

Using the measuring blocks on Vag-Com Field 8 is a value which the book Vol 1 
pg 24-90-2 says: "MUST fluctuate around an average of 128.  Value is 160.

So I'm leaning towards the O2 sensor bad............

Q:  Can the ISV foul this reading up.  I'm convinced the hestiation was from 
it (ISV) as the idle wildly goes up and down and stumbles and stalls upon 
start up without foot coaxing the throttle..........

IS the life span of these things (O2) a crap shoot?
Warranty?
TIA
-Scott by BOSTON