Fuel Problem Car Floods & No Start

I recently changed head gaslets in my '87 Z24 put it back together and it will not start. I noticed strong gas odor, checked the plugs and all were dripping with gas. I pulled the fuse on the fuel pump and it started immediately and runs fine until the fuel line empties! Some observations all the vacuum lines and vac pressure seem ok. I put a fuel press gauge on the rail and without cranking, key on only the fuel goes pressure goes up to about 40 psi for 2 secs and then drops to 0 immediately? Baffled any help would be soooo appreciated!!

Thanks much!!
Bob

Your IAC Valve is most likely froze up. It is just above TPS. Take it out push on it to make it move have some one cycle key it should push out when you turn key to off postion. If it does put back in cycle key again to reset idle postion. If that works you can either clean that one with carb cleaner or buy a new one