I have a 1999 Ford Ranger with 3.0 motor that I bought with a bad motor and I replaced it with one from another 1999 ranger. I also changed out the computers. Since changing motors when I start it first thing every morning it is a fight to keep it running for a couple of minutes then runs fine. I have pulled up on computer and it shows no error codes. Any ideas what could be wrong????

 

We will forgive you this time , but your in the wrong forum for Rangers.
Sounds like a simple case of the IAC sticking closed.
Remove it and do a cleaning with Throttle body spray until it runs out clean.
Be sure the Pintel moves freely because it's movement controls Idle air bypass.
It must operate or you will have starting issues especially in cold temps and deceleration stalling..
It needs to react to engine load changes at idle for A/C, power steering load, and charge system load changes etc.
Good luck.