My check engine light is on steady and my temperature gauge is at the 1/2 way point when it usually only runs at the 1/4 way point.

It's on the intake manifold next to the thermostat it will be the closest to the housing you can always disconnect the plug and run jumper wires from + & - and look at the temperature gauge to see needle movement or the light will be on steady

So did you check the gauge and the sending unit ?
Either component could be faulty.

the usual suspects are:
stuck shut thermostat
clogged raiator
dead water pump
low coolant level
it's sunday, rovers don't work on sunday.
Then again, maybe its wednesday, rovers take half a day then.

Have you checked your cooling fan to see if it is working propely? Let the car idle and get warm and listen for the fan to kick in (if they are electric) or just watch to see if the fan starts to spin faster if it is the old school type with a clutch. Have you replaced the thermostat? A bad one will let the temp rise since it opens too late and then the temp will drop off. But it won't due this only at a light and it will do it infrequently.

check for inlet manifold for leaks, also check cold start injection ( may be leaking)

I don't have the solution but I have the same problem. You are not alone. I have done everything you have done and have run out of options as far as fixing it with OEM parts. I am going to over ride the system with a hot wire and toggle switch and tie into the led wire on the #1 fan so when temp starts to rise past 180 degrees I can turn the fans on. Freeway driving is ok for me, no fan needed, just when I get off the freeway and around town engine gets hot. My toggle switch has a L.E.D. light in it to indicate the switch is on.

Could be the coolant temp sensor:



4.0L engine shown





5.2L engine shown



To test it:

Perform this test on a cold or cool engine.

1. Disconnect the negative (-) battery cable.
   
2. Unplug the electrical wiring from the sending unit.
   
3. Using an ohmmeter, measure the resistance between the terminal and the sending unit's metal body
   
   1. Infinite resistance or zero resistance: the sending unit is bad, replace the sender with a new one.
      
   2. Other than infinite or zero resistance: continue test.
      
4. Remove the temperature sender from the engine.
   
5. Position the sending unit so the metal shaft (opposite end from the electrical connectors) is in a pot of water. Make sure that the electrical connector is not submerged and only the tip of the sending unit's body is in the water.
   
6. Heat the pot of water at a medium rate. While the water is warming, continue to measure the resistance of the terminal and the metal body of the sending unit:
   
   1. As the water warms up, the resistance goes down in a steady manner: the sending unit is good.
      
   2. As the water warms up, the resistance does not change or changes in erratic jumps: the sender is bad, replace it with a new one.
      
7. Install the good or new sending unit into the engine, then connect the negative battery cable.
   

1. With the engine cold, remove the ECT sensor.
   
2. Immerse the tip of the sensor in container of water.
   
3. Connect a digital ohmmeter to the two terminals of the sensor.
   
4. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the sensor resistance illustration.
   
5. Repeat the test at two other temperature points, heating or cooling the water as necessary.
   
6. If the sensor does not meet specification, it must be replaced.
   

Submerge the end of the temperature sensor in cold or hot water and check resistance



Temperature-to-resistance relationship of the ECT and MAT sensors

check to see if you have voltage at the wire that connects to gauge, then check for continuity on gauge terminals to see if it's ok. almost sounds like it might be the gauge

check for blown fuse for gauges,light is a pro blem code,thatll have to be scanned to point at problem area.

The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine.
Fig. 1: View of the Engine Coolant Temperature (ECT) sensor Fig. 2: Engine Coolant Temperature (ECT) sensor locationTESTING
See Figures 3 and 4

1. Remove the ECT sensor from the vehicle.
2. Immerse the tip of the sensor in container of water.
3. Connect a digital ohmmeter to the two terminals of the sensor.
4. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the engine coolant sensor temperature vs. resistance illustration.
5. Repeat the test at two other temperature points, heating or cooling the water as necessary.
6. If the sensor does not meet specification, it must be replaced.

Fig. 3: Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor wiring diagram Fig. 4: ECT sensor temperature vs. resistance values