Citroen C3 1.4 Petrol - Citroen C3 Stalling going down a slop. - greenc3

I have a 2002 Citroen C3 since Oct 2010. However, when I am going down a slop or hill, it stalls when I put the clutch down when I want to stop. It doesn't happen when the road is level or uphill. I had the injectors and spark plugs all cleaned plus the engine has been checked by computer but nothing can be found. The car has done 70,000 miles.