car wont idle after headgasket swap?

i had a blown head gasket on my 99 gt, so we replaced the headgasket in my buddys garage, got a valve job and resurfaced the heads and threw on some headers, now with the car back together, we start it up and it wont idle for crap, itll die if you dont get on the gas, i though IAC, so i cleaned it and that made no difference. one thing i was considering is we do no have the passenger side header to midpipe connected all the way (it leaks because one of the bolts are in) could that cause all this? i find it unlikely, but i dunno. we checked all the vacuum lines, everything looks good, im pretty sure we got the timing right, just match the marks on the timing chains to the marks on the crank and cam gears? im open to any suggestions :D