I have a 1999 Dodge Ram 4x4 2500 Diesel with 170,000 miles. The temp gauge does not work, and it idles at 1100 instead of 750-800 RPM. I have replaced the Temp. Sensor Sender twice on the front of the block and a Truck Shop replaced the wiring harness from the sender, and soldered it at the connection.to the pins.

This started intermittently, only when it was warm. However, now it does it all the time. There is a slight hesitation at acceleration, but otherwise, it runs fine.

Thank you for any help!

 

See what the PCM thinks Engine temp is. Might just be the gauge itself is bad.

 

On a 99 you should be able to do an actuator test of the instrument panel which will move all needles around. If the temp gauge moves it's not the gauge itself but the PCM tells it to keep the needle at the low end. As HeyYou wrote, check what temp the PCM thinks it is. From the symptoms I'd guess the PCM doesn't get a proper reading.

Actuator test: Ignition off, press trip reset button and hold, turn ignition on, keep reset button pressed for 10s until odometer shows CHEC.

 

thank you!