Periodically my truck will not start when cold or damp outside. However if I spray starting fluid in the TB while cranking it will start. It will run rough for a few minutes and check engine light is on. Once engine idles for a few minutes check engine light goes out and truck runs just fine. I did install new fuel pump, fuel filter, and new air cleaner. Could it be the Idle Air Bypass sensor?
hard starting (cold) on 1990 Ford Ranger
I think that it is an issue with your fuel system. You spray starting fluid in your throttle body and that starts the car, which is a fuel substitute. It could be that your fuel system is bleeding down over night and not holding pressure, so it takes forever to get it started. It may be that the pump and all else is not totally dialed in, it may also be a weak fuel pump relay, that comes on after a bit of running. Did you use factory parts? I have seen really weird problems with some after market fuel pumps.
I had the same problem with my 1998 4.0 Ranger. The fix was a simple one for mine. Under the front of your vehicle is a crank sensor. If it isn't sealing properly it will not start in damp weather. When mine had the same problem, we, cert Ford mech and I, took to plug apart, cleaned it, and resealed it with some dialectric lube. Problem solved in my case. Hope this helps with yours.