LS1 Fails to start and run.... HELP PLEASE

I have an 89 944 with 2000 LS1 vette motor (stock). I purchased the car incomplete last year. The car has the stock Delhi ecu. The drive by wire was replaced with drive by cable prior to purchase. I installed, wired, new TPS, IAC and MAF as per pinout info found online. The injectors are new stock, the plugs are new stock and the coils are new MSD. The car will not start and continue to run. It backfires like crazy and shuts down. It sounds like the timing is off. In order to start the car I have to hold the accelerator to the floor and pump it till it starts then tether it to keep the car running. Pressure is at 55lbs. There is spark as well. Found out the ecu does have a factory flash and verified it by the company that completed it. Not sure of what else to check. Purchased another ecu just to see if conditions changed but they did not. Any help or guidance would be greatly appreciated. Thanks

any gm ecm is going to need to be reflashed to remove the factory security. the other thing here is you mentioned removing the electronic throttle and wiring in a idle control valve, the factory calibration isnt set up to work with an iac valve (it just opens and closes the throttle to adjust idle speed). no matter what your going to need to have a tune written for this combo.

the other thing id look at is your wiring. you may have coils wired incorrectly, id ohm out each coil trigger wire from the ecm connector directly to the coil connector, you could have a coil harness thats pinned incorrectly.