High acceleration - unusual solution
My high idle was a mystery on my auto transmission, 4 litre engine. Seemed to happen when the Jeep was warm, but could be cold, seemed to happen after it was started later on after having been run in the last hour or so, but not always... I replaced the rotor, cap, plugs and wires, that seemed to help but not as much. Hunted down a couple of vacuum leaks, but...
Oddly enough, when the Jeep was hot the high idle was more likely to kick in - when cold (less than 50 degrees temp outside) there seemed to be no problem, but the idle was low. Again, confusing.
I can only offer what worked. I began to discover that when I was stopped on a hill, and moving from brake to gas managed to roll backwards a touch... then the problem of high idle would come back the next time I started it. 1500 rpm minimum, sometimes over 3000 rpm... and yet, as far as I know there is no vacuum line going to the transmission such as there was on the older GM transmissions that had vacuum assist on the transmission. Is there?
When I stopped letting the Jeep roll backwards on a hill (and, among other things, stop creating havoc with all the little check valves in the transmission relay) the problem went away after a while. This just does not make sense, but when the usual suspects are ruled out such as ignition, carburation, fuel injection problems, throttle linkage jamming, the ECM keeping the idle up because the computer thinks there is a problem, then the highly unlikely becomes plausible. If this sounds out there, than just keep looking for that vacuum leak or something.