Gemini wont idle properly?

When i start up my rb gemini it revs straight up to about 3 or 4 grand and stays there. Ive tried reading up about it but havent found anything yet thats helped. I dunno weather its a vacuum leak or i need to play with the idle screws or if the choke is stuck on. I didnt do anything to make it start doing it i dont think i was just in neutral and playing with the air con and the revs just shot up. Now it wont idle properly whenever i start it the revs always shoot up. If someone can help that be awesome! its a rb gemmi fwd manuel carby izuzu motor.