Not wanting to run

I just did an engine swap, did an 03 g64 to a 05 4g64. Everything was plugged in, pipes, wires, hoses, bolts tightened right. But the car just won't sit idle, and I gotta put some throtle to keep it on, or else it stalls out. When I hold the throtle occasionally the rpms will jump, stay ab 1.5k above what I'm holding it to, then drop down. Idk what's wrong, any idea or suggestion?