I only get it when I put her in reverse after driving for a while, long enough for my automatic transmission to heat up enough to finally go into overdrive (it's not the relay or the solenoid, I have replaced them both). Anyways, I will come to a stop, say to park, and if I reverse into a spot, I have to give it reckless amounts of throttle and throw it into neutral just to keep it from stalling, and roll into the spot. When she does stall, I get 2-3-1. I have never gotten it at a stop sign, nor in drive, ever. Only in reverse. I have hesitation occasionally, but never when the car is cold. I do have rough idle at cold start, but it rights itself after 20 seconds (it sounds high, but there is no telling because my tach hasn't come in the mail yet) and the idle takes the car away in steady acceleration when I put it in drive from a cold start.
The MAF was replaced not long ago because it was burnt out by a faulty fully open airbox thermostat which has been removed completely.
The intake manifold has also been replaced recently.
The flame trap is new, replaced while replacing a loose vacuum hose.
The only other crack in the any hose I have found is the outer rubber around the fuel line going to the fuel rail from the back of the engine bay (it's a bad crack, all the way around, enough to see the harder line hidden inside, which is intact).

I have not tested anything else as I am consumed by a broken exhaust stud that occurred yesterday while changing the gasket (Haines manual lists the torque as 23 ft-lbs, which is too much, hence the broken stud. I have read on another forum that the volvo dealership manual lists 18 ft-lbs.)

In short, I figured my case might shake up some of the minds at work trying to find a common link in all of these 2-3-1 cases as they seem quite common. Only in reverse, after driving for a while. Why reverse?

I thought I would just update this thread. The exhaust manifold leak is cured with new studs, gasket, and such. It did help me find a small leak though. I believe it's too small to be any real worry, but it still makes my car sound like a damn tractor.

Anyways, about the the stalling in reverse after driving for a while thing:
It only happens when the gas tank is almost empty. Since gas prices shot up so fast , I hadn't filled it up all the way. But I filled her up yesterday, $50, and it hasn't sputter to a halt once since. I still have the rough idle at stat up.

How loud should a fuel pump be? In the endeavor to cure hard idle and stalling, I realized yesterday that my fuel pump is super loud. I usually have music playing when I drive, so I never really noticed it, until I heard it in between tracks. I thought it was my rear speakers. The speakers are fine. Is it time for a new fuel pump? and, Could this be contributing to stalling after putting her in reverse after a long drive?

A loud main pump could be from a dead in-tank pump or a bad rubber hose in the in-tank pump. The main pump is working harder because the pre-pump is not working. Dan

Try a good thorough cleaning of the throttle body and idle air control valve. Then make sure the throttle body switch and linkage is set properly. Dan

until you find the real cause, which MAY be the broken exhaust stud, allowing exhaust to escape, i would pull the fuse to the ecu, #4, i think. this clears the code and resets the adaptation. if this was never done but just the code cleared at the box, the bad habits the ecu learned remain. i been doing volvos, along with bmws and mbs, for about 20 years. i have NEVER found a real cause for 231 or 232. and i've got the volvo book for lh2.4 i think the ecu is too sensitive to the inputs and freaks out-sets 231/2. mercedes had the same problem with 94 or so cars with v8s that didn't have enough room in the adaptation range and set the light. their idea is to replace the ecu with a wider range to work with. 1400 bucks or so, i think. pulling the fuse on a volvo is easier. good luck, chuck.

I will give this a try after I cure my exhaust woes. For now she is parked with the exhaust studs, the ones that didn't come all the way out the first time I pulled the manifold (they didn't break, just backed out with the super rusted nuts) are soaking in PB. I have been meaning to pull the throttle body, even bought the gasket, but I just haven't gotten around to it. Been too busy with the interior and audio system I guess. I take it though that this 2-3-2 / 2-3-1 nonsense isn't than big of a deal in the end, my gas mileage is fine, and it's not interfering with the reliability too much as she starts right up. I haven't pulled my O2 sensor yet, just got to decide if I feel like soldering a universal into the factory harness, or buy the Bosch OEM replacement from FCP...

do not use a unversal o2 on ANY car. the sensor requires outside air , which creeps through the wiring itself, to work properly. a crimp or a solder job will close this path off. get an oe connector. good luck, chuck.

which creeps through the wiring itself

Where in the world did you come by this pearl of wisdom? This is not how the oxygen sensor receives ambient air, as an examination of an O2 sensor cross section will show.
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'80 DL 2 door, '89 DL Wagon

found in a bmw bulletin which date and title escapes me. it made mention of reference o2 available through the harness. this applies to the 3 and 4 wire sensors, not the 1 wire sensors from the 80's. IF i run across it, i'll post it. and so it goes, chuck.

It does not make sense to me. I use a Mustang sensor with a short lead, and I cut the crimped on mustang connector off and crimp a splice to the original 02 sensor wire. Based on the performance/fuel economy the spliced sensor works fine. The only issue I have is that the spice sits very near the driveshaft, and I worry about it getting torn apart but it has never happened.

I'll second that. I replaced the OEM sensor 10 months ago with the Mustang unit and did a very nice splice with shrink tubing and strain reliefs. No problem whatsoever, and replacing the "lazy" old sensor gave me a measurable improvement in fuel economy (about 3%).

FWIW, I work in aerospace and things that need to be vented are positively vented. I have a hard time believing that "leakage" to atmosphere through the wiring harness would constitute a positive vent path for the sensor. I doubt the automotive design world be significantly different.
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Thank goodness we don't get all the government we pay for. -- Will Rogers

Bad ECU.