87 4.3 TBI high idle

When started the idle flairs to 2000 rpm and stays there until engine begins to warm up. The car slams into gear and will do 35 mph like this. Coolant temp sensor is accurate, TPS accurate, IAC motor seems to be norrmal. Checked for vacuum leaks and found none. Nothing binding in the throttle body. I even tried a spare ECM that I have and it made no difference. I have never seen something like this and I am stumped. I am a pro with 40 years experience and all the tools and equipment. What am I missing here?

If you have a scanner that shows live engine data, can you see any reading that doesn't look right? Is idle and idle required the same?

Did you try blocking the mouth of throttle body to see if any effect on the idle, there should be a big effect, it should kill the engine. if no effect, you got false air getting in there from somewhere?

Just to add, I don't have your experience, I just didn't see anybody talking to you.

Unfortunately this car doesnt display like the OBDII cars with a desired idle on my SnapOn Solus Ultra. The problem only occurs upon first start up in the AM. As soon as it begins to get some temperature it slows down. I checked the car again since the original post. IAC at 19 when warm, block learn 124, timing 0 degrees with wire unplugged. I double checked for a vacuum leak. When warm it idles in park at 1000. Any suggestions look for when I start it cold? Thanks

Check what the pcm sees for cold temp. I would pull the iac amd clean it up makes it does not bind up also.

The sensor reads ambient temp on a cold start which has been around 55 degrees lately. The high idle happens only when cold. When the coolant gets to mid 70s it slows down. I already tried cleaning the IAC and even tried a new one I had in stock.