heres the deal, one of my friends got this swap done, they guy who did the swap used new wire harness with old computer, and also used old intake manifold. the idle is wacky upp, down, up, down. whats the exactly reason for this?? is it the old ecu? just a question it's not mine it's my friends just wondering

 

Sounds more like a possible vacuum leak or IACV problem to me.