Engine backfires when starting

Some history of what I have replaced.

I was having problems with the car dying after it had been driven for awhile, and not wanting to restart. It would restart if it had sat for awhile. Well I replaced the fuel filter, the injector o-rings and the IAC motor, the spark plugs and wires, fuel pressure regulator, all to no avail. I then replaced the ignition coil, and wa-la, the car would start, somewhat hard, and backfired once or twice when starting.

I tried to start the car the next day and the car was suddenly backfiring a LOT and would only start with starter fluid. It would run with high rpms, then as it dipped back to 600-800 rpms, it would die. If I kept feathering the accel it would stay running, and eventually after prob 2 mins of this it would run without having to feather the accel. Couple days later I tried to start it again and it would not start at all, starter fluid or no. I get constant manifold backfiring when trying to start, and it will run very rarely.

I am running out of ideas of what to check.I had a thought that maybe IAC went bad, which caused the backfire, which then blew the gaskets, so even when we replace IAC, I still get the backfire, but I'm not sure. This last part has all been conjecture, but if I remember correctly, the backfire when starting happened about the time when I checked IAC for problems.