Renault Megane 1.6 16V stalling problem?

My Renault Megane 1.6 16v 53 plate starts ok but when slowing down on approaching junctions etc it looses revs and then stalls. It starts up again no problem, the engine warning light has come on and the service light. It has had a full service on 24th May and the fault codes cleared, it needed some new sensors. We have a code P0335 message, crankshaft Position Sensor "a" circuit. Any ideas on how to reapir this? The car has had all ignition coils changed and also new dephaser pully. Please help!!!!