87 Runs poorly when cold

[GM 4 Life]

My 87 has a rebuilt older "orange motor" 305 in it w/ the complete 87 tbi setup on it installed from the po.It also has the 700r4 & 2:73 gears. The motor has less than 1,000 mi. on it. It has a new complete tune up, egr valve, coolant sensor, rebuilt tbi, new vac. lines, new fuel pumps & filter. I also verified the timing.When cold it fires right up, but then starts idling down roughly & stalls if I dont keep feathering the throttle @ 1,800 RPM'S or so. It also runs rough while driving /stopping untill it warms up. When it does die it always fires right back up. Once warm it smoothes out somewhat & has good power/pick up w/ no stalling, but its not what I'd call perfect.The outside temp. seems to have no factor on this issue. The fuel injectors werent replaced on the tbi rebuild & they have 255,000 mi. on them. Could that be whats causing this or could it be one of the emission sensors? I am @ a loss here & dont want to start expensive parts swapping on a whim. Thanks in advance.