1996 Mercury Sable Possible IAC Hiccup?

Engine Performance problem
1996 Mercury Sable 6 cyl Automatic 100, 00 miles

Problem has been persisting for a few months. When I drive highway speeds, and then get off the highway or stop at a toll and my RPMs drop, as soon as I accelerate my check engine comes on, blinking for a few minutes, and then turns solid. When blinking my engine idles rough. Engine codes say misfire on Cylinders 1 & 3. Have gotten a tune up and replaced coil, to no avail. The Ford dealership could not figure out what was wrong in their initial diagnostic and wanted an additional fee for further testing.

Since the cold weather has started, it is worse. The light still comes on under the same conditions, but now when I start my car it right away idles at around 1200 RPM, and doesn't feel/sound happy. Once it warms up a bit it idles closer to 750, but it takes a while to get there, and even just accelerating after a red light can see the RPM jump to 2300 - 2500.

I am thinking it might be the IAC. If I unplug the IAC while the engine is running the car does not stall. But I do not know for sure, and have spent enough at this point to be dissuaded from buying something as a means of a test.

Does it sound like the IAC is the culprit? Are there any other tests I could do to confirm this, or anything else I should be checking?