2001 Renault Clio intermitant starting problem

Hi, I have a cold start problem with my clio. It turns over ok and sometimes engages ok but mostly in the cold it only just about chokes into life. At this point I am pretty sure that it only kicks in on 3 cylinders for about 10 seconds before it recovers. A couple friends suggested changing the glows plugs which I have done but it still has the same problem. It is much better when it has been used for a while and runs ok when it has started. Any suggestions would be greatly recieved!!