91 w150 318 auto. So yesterday morning when I got in my truck for work it started and sputtered like usually so I hit the gas to get it going. After reaching normal operating temp I let off and it barely even idled. Put it in gear and it would barely even move. Didn't have time so took the wife Ford (ugh) to work came back at lunch and it ran no problem. Drove it to work and back home with no problems. This morning again same thing and at lunch again ran fine. These past couple days have been a cold spell around 30°f. It runs great when the temperature outside is warmer. When it barely idles it sounds like a cylinder is down (kind of like when you have the plug wires wrong). I've had this problem last November and I changed the coolant temperature sensor. That seemed to fix the problem until these last couple days. The IAC is shot and its unplugged and by pasted and has been for about a year now. I never had this problem till a couple months ago and I've operated in much colder temps before. Any ideas?

 

The IAC controls the idle. When you bypass it you lose its ability to provide a higher idle when the engine is cold or under load. I would look at the coolant temp sensor again for the no start problem.