bouncing idle? (searched)

Hey, this is for my brother he has a 93 gt, auto, with a mac maf and flows, he had some idle problems before where it was too low so we just highered it, but now when we start the car the idle is around 1000 but it seems like it wants to stall, but it is keeping the car turned on by reving kinda, it goes from 1000 to around 500-750, and just keeps going up and down, it dosent seem normal, do u think its just cold? or could he have some kind of vacum leak or timing or something, i tried a searched not much info out of it