A 1993 manual 240 with 140k miles. It runs good generally, starts well, no misfires, but throwing codes 113 and 232, O2 sensor and lean/too rich fuel mixture, leaking injector. Idle is too high, at 1,200 RPM. Also there is some slight stumbling, may be 20% reduced power. Now, all tune up items are good, and I just changed all fuel injectors all with no change in the above symptoms. Haven't dealt with the O2 sensor since I doubt it's the cause but may be I should change it... Ideas?

The 113 is the code that says "ECU is unable to put the mixture in the range where the O2 sensor can track it after much trying." Unfortunately, one of the most unlikely reasons, injector performance, was indicated in the early technical publications, before any real-world experience was gained. I believe this has resulted in thousands of unnecessary injector replacements over the years.

Much more likely is a gross failure in mixture control that is caused by something like a hole in the fuel pressure regulator diaphragm, or an oxygen sensor gone south. My recommendation always: (1) Reset the ECU by momentarily disconnecting power (not by doing the OBD code clear). Ensure the 113 comes back. (2) Be sure to check the vacuum port on the FPR for fuel. Then monitor the O2 voltage to see where it is, lean or rich, and probably not switching. Replace the sensor if you have no means of measuring fuel pressure or (3) check fuel pressure.

Disconnecting power to the ECU without disappearing your radio presets is easy if you know where the fuse is. In the early production '93, the fuse is #6 inside; in the late prod '93, its the one on the battery post labeled ignition.


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Art Benstein near Baltimore

With sufficient thrust, pigs fly just fine.

"Disconnecting power" via the fuse or battery. I have done it several times, codes come back. You don't mean while engine is running by chance?

You did it right.

No, don't disconnect while the motor is running. You merely want to clean the ECU of any stored trim adapting as well as the recent DTCs (codes) it has. When 113 is set, the mixture is rich for limping home, hence the poor performance. If the 113 returns after you disconnect power momentarily, then you know it wasn't a fluke such as can happen when a connector rarely doesn't make good contact.

There have been many different causes of 113, so it doesn't lend itself to the known symptom-cause table method of diagnosis.
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Art Benstein near Baltimore

I discovered I scream the same way whether I’m about to be devoured by a great white shark or if a piece of seaweed touches my foot.

Thanks, Art! Great as usual! (Still enjoying those two speedometers, operating flawlessly!)

If it is the original O2 sensor it is probably toast. Do an electrical test on it then you will know for sure.
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Will I buy another Volvo??? We'll see....