I need to know the nature of the O2 sensors used in cars....what should be the resistance reading across the sensors two wires or one wire to the body of the sensor, which screws into the header pipe......

what could cause the voltage readings looks 'normal' as in less than a volt, then flick up to 12 volts when running, and NO it's not a bad connection/ground/etc....

I even unplugged the heater core of the heated units, no change in operation.....connected or not, after running it and goosing it in the garage enough to get water up to the 190f region, the thing still jumps to 12 volts at the computer input, and no noticeable diff in engine running....

reason I asking is I have a steady on rough idle and BAD missfire that I can't find when driving it....

BTW, it's a speed density computer 1227730.......

 

I don't know the answer to your question. I consider o2's as maintenance parts and would just replace them. Dan

 

So you should never read any resistance on the O2 sensor output leads. It is similar to a Piezo element!
Now you will measure resistance on the heating element if it is a heated O2 sensor.
If you are getting 12vdc on the sensor output leads then you may have a short from the heater circuit to the sensor. Or maybe your PCM is at fault and causing the 12vdc reading.
I suppose if the PCM is in question you could completely disconnect the O2 sensor and measure at the PCM and see if you still get 12vdc, if you do then you know it is PCM related not the O2 sensor.

 

Well, that is what I just did, leaving the one wire to the computer, open ended and just the DVM connected, tried two different computers/same 1227730 and two programming modules....same reaction and of course, same rough idle....

 

So is your O2 sensor a 4 wire heated sensor? Or is it a single wire with the body of the sensor being the ground?
If it is a one wire sensor and you removed the wire directly at the PCM connector (basically eliminating the wiring harness as a fault) and you still got 12vdc at the PCM (and you tried two different PCMs) then it is possible that there is a pull up resistor in the PCM causing this 12vdc reading that you are seeing. It could be a bad O2 sensor. Now I am not sure about this as I don't know what year your car is and I am more familiar with OBDII PCMs.
My only other advice to you comes with my experience with some O2 sensors being of poor quality lately (not only O2 sensors but other sensors as well). You may want to try a different brand O2 sensor. I had good luck with the Denso brand on my cars heated O2 sensors. I did not have any luck with the AC Delco (Chinese made) replacements.

 

The oxygen sensor should be able to produce an oscillating signal averaging out about 0.450 mV once it is fully warmed up. It should go from 0.9 vdc down to 0.1 vdc and then back to 0.9 and so on all less than 1 volt. If the signal wire from the O2 saw 12 volts coming in I don't know what would happen to your ECM. As the O2 age their signal gets narrower and will start to lag behind the ECM's need for constant updates for smooth operation.

The O2's signal starts working slowly as the material used in the O2 warms up and in the early O2's they used Zirconium or something like that. It does not start oscillating completely and able to work until it was 600* (F). It is not a signal that is easy to watch with normal tools. I use a scanner to watch the O2 signal.

If it has a "heated oxygen sensor" then the system should switch to "Closed Loop" more quickly making fewer emissions doing it. The power it uses should not be relative to your engine issues. It requires 12 volts for the heater to get the sensor up to 600* (F) as well as heat from the exhaust to get that sensor on line. On the heated type O2 you need to be sure they have good clean power and a good solid ground and the signal wire should be left alone. It is very easy to damage or destroy an Oxygen sensor using carburetor cleaner or any type of oil spray. If your O2 is not producing an oscillating signal after 6-8 minutes that it might be time to buy a new O2.

I bought 4 Bosch O2's for a vehicle of mine and three were good and one was bad from the factory. I had to replace one at my local cost since they shipped me a bad one. Be careful where you buy them from as some people will not take them back once used.

 

I would never read the voltage on one because it oscillates so much, only the computer makes sense of it's ranges in closed loop operation. If you suspect it, replace it.

O2 would only affect idle when engine goes into closed loop, which is after the timers have expired, and generally when the O2 sensor reaches an oscillation range the computer recognizes.

More likely the idle is on the intake side, vac leak, IAC, etc. A misfire would be spark most likely, like a burnt wire boot.