1990 Mustang 5.0 takes forever to start

I got my 90 mustang GT in on a good trade. It has a BAD problem with starting. Almost like its got a VERY bad carb on it. BUT its all factory and fuel injected. Only thing thats been removed is the Smog Pump and EGR. problem is it literally takes almost 40 seconds of holding down the starter for it to FINALLY run, and when it does finally run it kinda backfires in the intake and and have to keep giving it gas to keep it running. But after it gets a little warm it idles and runs perfect. drive it 200 miles and runs great. stop at store to put gas in it and got to hold down starter for another 30 seconds before it finally cranks back up.

When i got it it had no O2 sensor harness on it. thought that was what was wrong with it. finally found one and bought it and hooked them up and still took forever to crank, but problems got even worse, after running for about 5 minutes it starts missing BAD from idle to about 2500 RPM then runs Like a new car. So i unplugged them for now. But i got to get those fixed also.
The car has a new Temp sensor on it, New IAC valve on it, Just tested the tps and it checked out perfect. Its got good fuel pressure to the Shredder valve. Spark plugs and wires and rotor button and cap all look good. Any one have any idea what could be going wrong? I would REALLY appreciate it if anyone could give me somewhere to look. I dont want to have to take it to a shop, but its not looking too good as of rite now.

PLS HELP!!!:?: