When l turn start the ignition, the car has problems maintaining the revs, it should tick over at 1,000, but it stutters/fluctuates/oscilliates, or whatever you wanna call it. It sometimes just has problems, sometimes has none at all and sometimes just stalls. Also a light on the dashboard lights up.Please help!

Unfortunately l cannot answer your question but it would be interesting to see any replies you get because l have exactly the same problem with my saxo. The garage has told me there is not anything wrong but l think there most definitely is!

l am going to guess at Idle Control Valve, or Stepper Motor or Idle Air Valve.whatever Citroen like to call it.
It works to regulate the air going into the engine when idling & when it goes faulty makes the car 'hunt' for the idle spot & sometimes stall.

Should be located somewhere on the throttle body or inlet manifold.normally held in by a couple of bolts with a rubber o ring as a seal.
O ring needs replacing whenever it is taken out.
Sometimes the ICV can just be gunked up & a shot of carb cleaner does the trick, other time is it is a case of a new valve. Not sure how much these cost on a saxo but on a mg zr they r about £85 new so u will be looking at around that amount.

Could also be an injector blockage or fault.

My advice would be to give the car a shot of redex injector cleaner.available from any decent motor factors or failing that Halfords. If that does not help arrange for the car to be given diagnostics to check for any stored error codes.