2000 Renault Megane 1.4 16v?

Hope you can help!

I have a 2000 Renault Megane 1.4 16v Sport and occasionally when idling, the engine will rev up and then settle back down. The engine warnming light and "STOP" will appear on the dash.

The lights sometimes also come on whilst driving, then go out a coiuple of seconds later.

Are these two incidents related? What can I do to fix the problem? Has anyone any ideas? Thanks in advance!