how can i fix my 2003 new shape renault megane?

when engine cold or cool there is clattering sound when engine start pressed. The clattering disappears and car drives ok when running. When cold and start pressed in addition to clattering sound the car does not start. Usually starts on second attempt. There also appears to be additional exhaust emission when engine started from cold. Problem has been ongoing for few months. Starter motor has been changed but did not solve problem. I would appreciate any help. Thanks

clive
June 2010