Dodge Intrepid Coolant Temperature Sensor

1998 Dodge Intrepid 2.7 Engine Rough Idle And Trouble Starting When Car Is Hot?? Just Replaced The Ect Sensor Still Doing The Same Thing.....

The Car Will Spike The Temp Gauge, Then Go Back To Normal. Does It With No Rhyme Or Reason. Should I Replace T Stat? If So How Do I Go About...