duty cycle drift

[Konstatntin Bogach]

I was measuring FV duty cycle at different conditions (not driving) and
found strange drift. At start and cold engine it is stedy 65%. Then it
slowly moves down and at ~50% it goes to closed loop. Now it changes in
45-55 range. Bridging contact 2 and 3 on trottle switch connector (WOT)
send it to steady 62%(open loop). Looks good?
But after 10-15 min of playing with it I found that at closed loop duty
cycle is shifting toward 40-50% and stays there. What it might be?
Something causing rich running?

I did it first time and I have several questions.
I pressed repeatedly "hold" button on multimeter to see the range of
duty cycle cause it was changing continuosly on the screen. I saw posted
messages saying that people observe duty cycle while driving. I doubt
they used the same method I used. What do they use?
Another question: using same method I measured O2 sensor output voltage.
It is between 20mV and 2.2V. From what I read I expected to see ~1V as
upper value. And I though all of them has same output voltage. Any
ideas? 

Thanks.

Kosntantin Bogach
200tq 89