engine idle

[keeff]

Hi folks ,need some help, the idle on my 4.2 is around the 1000rpm mark, but when the engine is warm it will jump up to about 1250 rpm and stay there for a while the drop back down again,it will keep on doing this. The car wasn't used for about 10 weeks and this problem has only started happening since then. Has anyone got any ideas ?

[touching cloth]

Sounds lambda-ish to me.... then again I am a bit of a mechanical numpty so who knows