ground to ground should be 0ohms. Probably conector resistance. This is probably not enough to cause problem. Clip a direct ground to test difference. 1 is ground 3 is 12v supply voltage to sensor 2 is output pulse to ecu and would be seen as 5 volts though if you put it on a scope you would see the sharp rise and fall from 12v to ground. Pulse frequency varies as rpm is increased.

Idle problems-

unmetered air- vac leak, egr valve leak , throttle body venturis clogged

ecu temp sensor- check with ohm meter