Renault Megane 2004 1.6 revs dropping when first starting car

I have a problem at the moment that only arises when I first start the car. It lets me pull off fine no problems, but then the next time I push the clutch down to pop it into first gear at a standstill the revs just drop and the engine cuts out. This happens probably 50% of the time when I first start my car in a morning. I have changed spark plugs, and coil pack, any ideas anyone? Thanks