I have been ignoring this thread because of the title. I saw it was getting larger and larger and thought I would see what is going on in here.
I can tell you that idle solenoid thing on the carb is a little DC motor. It controls the idle speed via the computer. I found the Ford adjustment procedure somewhere in my books, I can try to dig it up again, but I can tell you it is very complex. You have what you would call the idle stop and it has a certain adjustment, and then you have to mess with the computer and do a procedure so the computer sets the idle speed to 2000 rpm,, and then you adjust that little motor till the engine is running at 2000 rpm. There is more to it than that, but that is the jist of it.
I also had high idle problems when I first got my 1984 with the 2.8 and all this junk on it. It would idle beautifully, and then all of a sudden the idle would go up and it would start having a miss-fire to it. I found out for some reason the computer would suddenly advance the timing and cause the high idle and the miss-fire. I pulled the computer codes, I had so many I said the heck with it, and converted to the duraspark II distributor. I am still using the original computerized carb. It runs so good now and idles so smooth.
The only real problem I have now is with the choke. These carbs have a full electric choke, I am getting power from the white/black wire off the alternator. That works great also. But, this carb only has one high idle step for the choke. All the other high idle steps where done away with, the little idle motor did all that with the computer and the temperature sensor. So at first start everything is fine, I get a nice high idle. But soon after when the choke starts opening, the idle drops down too low, there are no steps on the fast idle cam and it wants to run a little rough and stall till it fully warms up.