Hyundai Repair: 2001hyundai sonata gls v6, coolant temperature sensor, throttle position sensor

Question
when the car reaches tempiture in town start & stops the engine will rev up for no resone at a stop  if on the highway it runs fine. at a stop it acts like the tempiture fan tures on and the engine starts reving up and then idiles bake down. what do i fix?

Answer
It'll probably require a scan tool to check the data feeds from your various sensors to locate the issue.  My primary guess would be perhaps a defective coolant temperature sensor.  If it reads too cold, the idle may increase.  But I wouldn't recommend simply replacing the sensor unless you have some sort of significant evidence it's defective.  A defective throttle position sensor could be another cause.

If your check engine lamp is on, you'll want to start with checking the trouble codes.  The first trouble code stored in the PCM will have freeze frame data associated with it.  This data represents some of the readings at the time the computer recognized the problem.  If your coolant temperature sensor reading at the time was too low, that would be a significant indicator that your coolant temperature sensor is bad.