Check your intake manifold gasket, did you put a new one on when you built this? what I see happen is, add a turbo the intake is now pressurized, an old gasket cracks and leaks, idle high or surges. Also, since this is not a kit, if your blow off valve just dumps under the hood, try hooking it up to the air intake tube, yeah I know it wont sound cool but see if this cures it.

madmike...