1997 Renault Megane Fast idle

I have a renault megane classic, when I come to a standstill after driving at any speed the engine runs fast idle, I don't have a rev counter so I don't know what it is, I guess it's around 1500 rpm. The revs do not come down even when I switch the engine off and on. It is more prominant when I stop the car with the steering on full lock. I have cleaned all parts, but I have no idea what needs to be replaced.

Thankyou.