Coolant temp problems

[2000S4]

I am having a problem with my coolant temp. If the car is sitting idling it will go to the middle mark of the gauge. Once i start driving the gauge needle will drop. If i sit at a traffic light it will start to creep up. What do you guys think the problem is. I replaced the temp sensor.
Thanks in advance

[S4 in_lowplaces]

it's supposed to go to the middle. Just not past it. if you drive you have cool air being drawn in which cools it down a bit, thats all your noticing.

Even though Mine does go past the middle line, I think my after run fan is dead. Anywyas I woultn worry to much.

[Rated S]

Thermostat is broken. I have same problem. I've replaced my temp sensor 3 times (this being the fourth sensor) and it still doesn't work. It throws a CEL when I use heater, telling me either Thermostat or Temp Sensor is broken. When I use heater the needle just stays 'down' and doesn't move.

[JayyyyyC]

I've noticed that after I shut my car off after driving, if I turn the ignition on and get the gauges to turn back on, the coolant temperature is past the middle mark. When the car is actually on and running, coolant temps are right at the middle.

[obijohn22]

thermostat is stuck in the open position and is not able to regulate the water flow, too much flow =cooler temps.

[The_Jerbel]

^^Agreed. Sorry bud, but it's time for a TB/WP/t-stat job.