What is happening over 4000rpm?

[wawa]

What is happening in our engine over 4000rpm? I'm asking because I have an intermittent problem that I cannot find. When I push a little the engine, I often but not all the time have the engine cuting. I lift the gaz and its ok, run fine. It feels like ignition cutoff. I have change twice the MAF and twice the AOS, but still the same. I have no CEL code, and engine idle smooth and run smooth under 4000rpm. But over, it sometime cutoff, sometime not.

I know the variocam are activated at about 4000rpm, could it be related? How does it work? Could it be something else? Any idea or suggestion?

Model is a 2000 S

Thanks
Chris