My 1992 3.0 5 speed has this same issue. Here's what i see on mine.
I have no codes from KOEO or KOER. WHen it's stone cold, it idles correctly. As soon as it warms up at all, it heads north of 2000rpm. I replaced the IAC with no change. I notice that if i disconnect the IAC when the idle is high, it immediately drops to about a nice even 700rpm which tells me the computer is telling it to idle at 2000rpm.
WHen i run KOER or cylinder balance test it all works correctly. In fact, if i insert my test jumper, the idle drops. It also dropped to normal when I pulled my timing spout. Timing is set to 8 BTDC.
At lunch today i will be cleaning my EGR though I doubt this has anything to do with my idle. I also have not tried my A/C to see if that has any effect. I will check that today too. Anyone have any idea why my computer would be telling my truck to idle so high?
EDIT: I went out at lunch, i have no EGR. THere is a block off plate. I ran my KOEO and KOER and got a 172 and 176 in my KAM but the engine idled fine. friggin fraggin frocken, frigger. This thing is driving me nuts.