Well I dont think it would be a bad ECU. If everything else works like that, and it makes it turn over.
Cam/Crankshaft position sensors maybe....
What about fuel choke? You said its getting fuel, the pump is
working and everything? Cuz that could caus an instant stall too...
What about not enough back pressure because there is no exaust...other then downpipe.
Is the intercooler hooked up completly?
Not enough air? Too rich? Hard rough idle? Try revving it just a bit as soon as you start?
Call any mechanic?
Here are a couple links I found not 100% the same issue, but somewhat similar.
IF ANYONE else has info PLEASE PLEASE post it.