[T3] Cold idle Problem

[SCS Crewcab]

I got my '71 FI Fastback running. I plugged the holes in the gas tank 
with epoxy paste and squirted carb cleaner in the ports of the fuel pump 
and kept reversing polarity until it freed up. It's running pretty good 
for being parked for 3 years. Kind of amazed it cranked at all. Anyway, 
I've had a nagging problem ever since I got this car. When I start it 
when the engine's cold and let it idle, it either shuts off or idles 
like it's about to shut off. If I rev it up a few times or just hold the 
pedal down about a quarter of the way, after about 15-20 seconds, it 
will idle normally. I've tried all the obvious things like timing, 
plugs, plug wires, idle setting, etc. It's no big deal, I'm just 
wondering what's causing it.