can faulty temp sensors cause high idle?

my car had a prob with staying cold so ive put in a new thermostat. now it warms up but never above half way and the car has been running for nearly an hour at times on the drive. that could be the sensor for the gauge i guess......but.....if the other sensor (to the ecu) is faulty could this cause a high idle and running rich. my only other option is o2 sensor but thinking about the temp sensor first?! any ideas?

 

See your other thread. ECU temp sensor is likely culprit - best check for error codes.

 

Mine never goes above half way...why would you want it to?