1988 Integra runs rough. Oxygen sensor code

I have a 1988 Integra with about 150k miles. In between fillups on a road trip this year the car was all of a sudden running rough at idle. And, it stumbles slightly during initial acceleration. I also
noticed at least a 15% reduction in highway fuel economy, though at highway speed the car still runs fairly smooth. All cylinders are firing.
The engine light occasionally comes on now for a few seconds then back off, usually at idle. Idle speed is normal, and I've actually adjusted it up due to the rough idle. Since the trip I have replaced the plugs, cap, rotor, and air filter. I have since checked the ECU and it indicates code #1 (oxygen sensor). Now, what exactly is this telling me about the sensor? Is it possible to get this code due to other conditions if the sensor is in fact still good?
When changing the plugs I noticed that number 3 was unusually black (carbon). After a couple weeks with the new plugs, number 3 is again blacker than the others but still firing fine.
I've reset the ECU and waiting for the next occurence. Should I just replace the oxygen sensor? Any other ideas?
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Bad idea. A band-aid fix at best.

These old OBD systems only set an oxygen sensor code if the sensor reports an out-of-range signal (less than .1 or more than .9). This can occur if the wiring/connector is corroded or frayed. The sensor only outputs a max of .9 volt, so wiring/connector integrity is crucial.

If only #3 is black, then you've got some sort of problem specific to that cylinder. Replacing the oxygen sensor won't fix that. Time for a compression test and for making sure the spark is actually and reliably making it to the plug gap.
Do you have EGR?
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This was just to keep the engine from dying at stop lights.

So, does this mean that the error code is telling me that the sensor is indeed going bad? I wonder if it could be going bad on the rich side, causing my poor fuel economy. I will try to put a volt meter on it. The electrical coupling is indeed coated with leaky oil. I will clean it up and see what that does.

There is no EGR as far as I can tell. No pipes to or from exhaust and intake manifolds. Nothing that looks like a big EGR valve as shown in your EGR photos. Only the oxygen sensor is attached to the exhaust manifold.
I'll try a compression check, although the engine doesn't skip/chug as I would expect it to with a bad cylinder. It just runs rough consistently.
Thanks for the info.

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wrote:

Still a lousy idea.

No. It means the connection may (or may not) be poor. I have no idea if you're using an OEM sensor or an aftermarket one, and I have no idea what kind of electrical connection there exists between the sensor and the ECU.

Won't help. You need a Digital Storage Oscilloscope (DSO) to properly diagnose an oxygen sensor.

Oops. Got a leaky valve cover gasket, evidently.

Better to find a good Honda-specific garage, scarce as those are...
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