OK - now take IR thermometer and measure at the radiator top, where top hose attaches. In the pix I have the dot on top, it seems to work better just on the side about an inch down. This will show you when warming up that thermostat has not opened yet. When it opens, this spot warms up pretty quick.

Now, since you revealed that the scanner readings were taken within two blocks of the Disco Domicle, that could explain why coolant temp was in the 120's. Coolant temp when fully warmed up should be closer to or slightly above thermostat rated temp. When re-installing, if the stat slipped down just a fraction of an inch, it will leave a large always open path for coolant flow, and keep things cold, and mixture rich.

So with an ir you can check this next time you go for a test drive, no wrench required.

How is your idle now? Smoke when?

 

ET - here's some pix for reference.

 

Thanks Buzz I'll take a look at those.

Idle is still either too high or too weak. High idle is between 1500-2500. Still smokes until engine really warms up.

 

My high idle was IACV related (cleaned, replaced, replaced), and my ECU would not re-learn, no matter what trick from various forums. Swapped ECU and it works. Driving with high idle is tough on tranny, taking off from standing stop, etc. ....