I had the same problem. Is it leaking coolant or anything from the intake manifold gasket? Mine was and it turned out that I didn't remove the old intake manifold gasket well enough and it was leaking air and coolant through the new one. Did the throttle cable go on right?

It is most likely the intake manifold gasket since that is the only place enough air can get into to cause this. Unfortunately, if it wasn't scraped off enough if it stuck to the head, you may have to pull the head again if you can't remove it all.