Citroen

When we are de-acclerating the car when it hits 1 (1000revs) suddenly decides to drive on its own. ususally in about second gear! have been told by the garage that car is designed to have a ticking over system to stop it stalling. i can understand this and understand possibly it would suddenly accelerate a little but with us the car takes over and can be hard to keep a slow speed. is this normal for this car or has anyone else had this problem and know what is happening? thanks

1.) idle speed out of adjustment 2.) engine oil seeping into cylinders causing the engine to run extra on engine oil. 3.) some sensor malfunction does this help any?