I have an '08 T&C with the 3.8l with 190k miles. Been dealing with this for months to no prevail. First upon start up it idles high up to 1250rpm then will come back down with in a couple minutes but that's not the big issue. While sitting it will come up to temp fine but when start driving it falls back down to cold and doesn't register it and then there's no heat. It will do this for awhile then stop for awhile and then come back. It also sometimes very frequently and sometimes not will turn the electronic throttle control light on, it will stay on until turned off and sometimes it's on immediately upon starting and sometimes not. Also sometimes when the etc light comes on the cruise control doesn't work and yet sometimes it does. The only codes of any kind is for the coolant temperature too low. The following has been replaced already:
- radiator cap- upper and lower radiator hoses- ambient temperature sensor
- coolant temperature sensor- battery- tension pulley assembly &belt- harmonic balancer (due to failure)
- starter(due to failure)
-thermostat
I am at a loss and have run out of knowledge for this issue, any help information is greatly appreciated, ty.

 

you have a broken thermostat

 

I forgot to mention that the thermostat was new as well however doesn't mean it's not a bad one but how would that relate to the electronic throttle control?

 

did you install an authentic OEM thermostat? They’re like $35 shipped. No sense going aftermarket. I would also consider looking at the water pump. Maybe that has issues. The tip off is that you’re sometimes not getting heat. A failing water pump will not produce heat.