Sounds familure....
I know you said before, mention anything and everything possible, no mater how simple it may be.
The car i've got does the same thing if you don't gas it right, but if you keep at it i can get it to start, and run. It never gets up and goes the first time. Backfires about 2-3 times then dies. But if you keep on the gas and rev it for about 10-15 seconds and let it go. The idle drops off to about 600 rpm then fixes it's self and runs.
You may have a more severe problem then we had, and Febo and i have rounded it out to 2-3 things. BISS and ISC motor both being bad, along with ECU about to go out on us.
Double check timing, fix the grounds if you can find any, if not make some of your own. And let us know how everything works!!
Also, do you idle surge, or did you iddle surge on the old car? And what all got transfered from one car to the other?
Was it just an engine tranny ONLY swap? If so some of the above items may be totaly shot. also, vacuum lines. They could be cracked, pinched, or otherwise missing.