Have you tried adjusting the IAC's cold start idle. There's a screw on it that allows you to apparently allow more air through when cold.
Mine stops spluttering if I push in more cranking injector time at 10degree's. From memory standard is 24ms, I pushed mine up to 35 and it starts instantly. But thats on a PFC. My stock ecu did the same but obviously not remaped so I wasn't able to test.
Its normal for the o2 sensor to read rich when cold. Since I put the new genuine o2 sensor in it reads 3.98v when I first start the car, then as it warms it quickly drops to 0.2-0.9 and begins cycling.
It can't help doing a vac/leak test. Grab a bit of exhaust pipe, weld a top on to it, 2 t-bolt clamps, either an aircompressor attachment screwed in to the top or drill a hole and use a tyre valve, remove the afm to compressor cover pipe and place the little tool you just made on to the front of the compressors inlet. Spin the motor over to TDC and compress the system to around 10psi. Soapy water and spray it looking for bubbles. You can also use a piece of fuel hose shoved in your ear to listen around the IAC and those hard to get to bits (inlet manifold etc)