Engine over revs and can't be driven

Hi help needed ref Renault laguna 2003 2litre petrol
First rev counter wavers up and down when slowing down
Secondly on long journey revs suddenly fly up to 5000 revs but no increase in speed if I pull over and go down gears and pull away it was ok for awhile
Now service light tracking light and electrical fault light comes on. After driving or running engine for 20 mins or so lights come back on engine revs to 5000 and engine goes up n down in revs. If you press accelerator no response also wTer seems to be disappearing via scaife either steam or water droplets.I have changed throttle position sensor the potentiometer and had the ECU checked ( no proplem with the ECU working ok)
So please can you advise me?