My nephew just bought a 99 civic cx with the stock motor in it. While driving the car temp guage goes up and says its hot but the radiator and hoses are still cool. I believe it is the thermostat but I am not sure. What do you think?

Also the car idles fine but after driving it idles up and down, up and down, up and down. I have no clue what this could be but thought maybe it has something to do with the temp of the car as it might be sending mixed signals to the ecu causing the fluxuation in idle. Whats your thoughts?

 

change out the thermo..

I would start with the cheap parts 1st then work ur way to the water pump if needed.


The flux is probably the IAVC on back of manifold.

https://honda-tech.com/forums/acura-integra-6/%2A%2A%2Ahow-clean%2A%2A%2A-your-iacv-k-idle-air-control-valve-1575913/