coolant temperature sending unit

Hello I have a 94 3.4 camaro.Here lately when I crank my car sometimes it idles at around 2000 rpms in park and 1500 rpms in gear.I can turn it off then back on then it acts normal.(guage works fine)I was told this could be the coolant temperature sending unit.Does this sound like the culprit and do you have to take it out of the car to check it.I did the ohms test while it was in the car and it was way off.I put one of the leads on the unit and the other on the positive battery cable is this right.Also to make sure there is only one of these coolant temperature sending units on the 3.4 camaros.
Thanks in advance for any help.

Do you have a check engine/SES light?

No there is no light.

It could be something else so if any one knows what could be causing this problem please help.
Also I am checking the unit on the front of the left cylinder head.Is there another unit that tells the computer what to. could it be the coolant temperature sensor that would cause this.

Someone please help me this is really bugging me.

I cranked up my car this morning and it is now runnining rich with a rough idle.Is this related?
(plugs and wires are new)

I cleaned out the IAC valve and now it seems to be doing better.It is idling smooth.