Upstream O2 sensor reading

Hi,

I have a 2003 VW polo. 

I was testing the upstream 02 sensor using my uscope master.  The engine was warmed up and in closed loop.  

At idle, all was expected,  02 output fluctuated between 200 mv to 800 mv. 

When i raised the rpm to between 3000 -4000 rpm, i had expected to see the 02 stick to 800 mv.. however,  what i actually saw was it continued with the same fluctuation between 200 to 800 mv, the only difference being the frequency of this changing increased significantly.  Its this normal operation ? I thought that the 02 is fixed rich at high rpm?

To be clear,  there is no performance issue or codes on the car, I  doing this testing purely for training purposes, 

Thanks for any help 

Its this normal operation ?

Totally normal operation. 

I thought that the 02 is fixed rich at high rpm?

I think what you're talking about is power enrichment? That only happens during wide open throttle and/or heavy acceleration. It (generally) has less to do with engine speed and more to do with engine load.

Raising the engine speed off idle while parked isn't going to tick all the boxes for the ECM/PCM to enable power enrichment. Also normal operation.

Perfect, makes sense. Thanks very much for the response