High Idle at Cold Startup is Gone

1993 Toyota Land Cruiser.

Ever since our first "cold" morning here in Missouri in October 2015, my Land Cruiser does the following on cold startup: cranks just fine without hesitation, revs up like all is well for about 1-second but then the RPMs take a dip to almost a stall before regaining composure and leveling out at around 600-650 RPMS which is the warm idle speed for this engine. A cold engine should not be doing this. For the previous 6 years of ownership on a cold start, it will crank and rev to 1200-1400 RPMS and slowly back itself down to a warm idle speed of 650 RPM over the course of 5-10 minutes if left to idle. This would be the normal sequence. I have no power loss and it runs smooth. I am very well-versed in 80 Series Land Cruisers and have done countless troubleshooting tasks per my Toyota FSM. Close to 100 Cruiser guys (also well-versed) on another forum have chimed in and we still have not figured this issue out. I've replaced several parts with loaner parts from Cruiser friends and nothing has changed. I will leave out everything I have tried at this point as I don't want to rule anything out. One other thing I've noticed is that when I disconnect the battery or pull the EFI fuse to reset the ECU, I get no relearning period whatsoever over the course of the next several drives. It starts up and behaves just like I've posted above. Normal behavior would be a low, rumbly idle as the ECU relearns things. It's almost as if my ECU is stuck in a constant relearn mode. Hard to say!

Thanks!