Scenic idle problem

I have a renault scenic 2001 1.6 16v that runs fine when driven but will not idle, as soon as throtle is released engine runs erratic at about 1000rpm until it drops to 500rpm then stops, have checked for inlet manifold leaks and not found anyhing, ignition coils are ok, plugs are burning red/brown, also when engine is cold runs fine, only starts bad idle when up to norm temp

many thanks gaz