I am getting a code for P0125. It appears that I may have a stuck open thermostat. The vehicle warms up in 4-5 minutes (starting to warm up) in 25 degree weather. The electronic display never exceeds 3 bars but normally it is 4 bars on the digital display. I am not sure if I need the thermostat or possible new coolant sensor. I am not sure if this problem is related or not so I will describe.

In hot weather after driving for 30 minutes or longer in just hot weather above 90F. If I stop for 5-10 minutes and crank it up it will immediately go to a low idle to the point that it will almost die out.

Appreciate all your thoughts.

 

For the cost of the thermostat and it's replacement there should be no question or concern especially if the vehicle is more than 3 years old. By that time it's time to look into coolant replacement also, to help lessen the possibility of internal corrosion.
The thermostat rating should be in the area of 195 degrees F. Once that is done it will eliminate that possible cause from the concerns.