Renault Laguna wont hold idle and wont start without revving while start up

my laguna has always had a prollem with low idle and sometimes cuts out while gearing down coming to a junction but today everytime i started it it idles very low before cutting out completly and now it dies instantly after start up, it will stay running if i rev during start up and hold high revs but when i let off the accelerator it just dies instantly again ! ive had a few suggestions of idle control valve being gone and another of tdc sensor gone..... any help much appreciated Thanks !