early 95 with stick and only one o2 sensor. Only 1 o2 sensor wire too. I'm not sure if the car needs proprietary equipment since it's not odbc II (translated where to take the car or what Motronic test equipment I should ask the shop to prove they have before I waste my time with the unqualified.)
The test results (done 3 months ago)
We've updated the equipment, and averages for the 2.4L are based on oil run ~6,000 miles. With that change, iron (from steel) is higher than expected for a short oil run like this, but it's not something to worry about. Iron has been stable so far, so this level may more or less be the norm for your Volvo and the use it sees. Sodium could show coolant in the oil. It's just not enough to be sure at this point. The viscosity is a little low, but neither that nor the 0.8% fuel is problematic. Check back on iron and sodium - we'll know more about sodium next time.

I'd like to share that my 850 problems of running rich, stalling in the summer and also giving some lean codes is probably related to the air hose between the air filter box and the intake manifold. There might have been little holes in it that i didn't notice for years but I couldn't help but notice huge cracks in it this month. The MAP , mass air flow or whatever sensor is before this hose in the intake chain so it possibly got to the point where there was no air passing through the sensor or air cleaner. I wasn't driving the car much which is good if there is no air filtration.

I got a new air hose, seems to be much better. The check engine light has stayed off. The is pre- ODBC so diagnosis was limited.

Cracks in the throttle body hose would definitely cause the issues you described. Because the air volume is changed by cracks in the hose it would consequently cause the air mass sensor to give a bad reading to the ECU resulting in an incorrect air/fuel mixture and drivability problems.
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Will I buy another Volvo??? We'll see....

Even under normal conditions, oil viscosity can go down as some of the oil molecules are torn apart in the engine.

If you are worried, shorten your change mileage to 4000 miles and see if that changes things.

You might also try to see of winter is the cause of this issue, consider changing your oil in the spring.

Well I drive so little it's usually only 2500 miles or even 1800 between oil changes. Bigger issue would be ruining catalytic converter. So ultimate issue is how are these pre-odbc2 volvos diagnosed. Propriatary computers only volvo dealers had? Yea i'd like to diagnosis not throw parts. 02 sensor (i only have one dispite protests to the idea). Maybe just a coolant sensor. I do the little underhood boxes by the headlight and get no errors, but live data might show my temp sensor thinks it's -40F farenheit. So the beat goes on. No point in taking the 850 to a shop that doesn't have the proper diagnostic gear for such a non odbc volvo.

You can test the coolant sensor. Unplug it, probe the sensor ends with a multimeter and check resistance. A cold engine should have high numbers and a hot engine should show resistance of about 250 or less.
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Keeping it running is better than buying new

I would look for an independent Volvo shop who specializes in older Volvos. There must be one in Westchester county or metro NY somewhere.... Somebody out there must be familiar with the OBD-1 cars.
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Will I buy another Volvo??? We'll see....

Just an FYI. I replaced both O2 sensors on my turbo 1995. The error codes went away, EXCEPT when my daughter used it to commute to work. Everyday, my daughter would come home with the CEL on and I would clear it. I finally asked her if the CEL came on the same place each commute. Yep, in stop and go traffic at idle speed. The code was for a failing CAT, which I recreated while on a long trip around the neighborhood.

I let the car run between 5-10mph for a few minutes and the CEL came on. I attribute that error to be the diagnostics in the computer, not in anything that is repairable. A 1,000 mile trip will not trigger the code, but I cannot drive at idle speed in 1st or 2nd gear.

As for finding a mechanic/shop that can diagnose your error code, lots of luck. The dealers have no one that remembers what an 850 looks like, much less how to use the A&B code boxes in the engine compartment. A computer cannot be plugged into the car, if your car doesn't have a port next to the cigar lighter. If there is a port under the coin tray, a Volvo scan tool can be used to watch the O2 sensor operate.


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Keeping it running is better than buying new

My main concern is just diluting the oil and ruining the engine. I will test the 02 sensor as you document, if i can get it out.

25 years ago, right after the warantee ended the dealer told my my exhaust manifold has a crack. I recently read that that can draw in extra 02 and fool your computer into think it's running lean.

I figured there must be some proprietary and obsolute volvo test equipment for my 850 that maybe i can find on ebay someday. I just found out for an old audi i could benefit from someting called vag-com (va = volks america?). Some old ABS test equipment seems to go for a fortune on ebay though. Time is on my side.

Any 'crack' in the exhaust before the O2 sensor can cause a lean condition. Soapy water on a cold manifold might make the dealer a liar? Hard to believe that a crack didn't grow over 25 years!

Most parts stores will loan you a 7/8 O2 sensor removal tool. Yes, lots of PBblaster and patience. Getting that thing to move initially is hard, and you may have to tighten/loosen the sensor a lot of times before it comes out.

Volvo uses VIDA/DICE, but it needs an OBDII connection.
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Keeping it running is better than buying new

Running rich does not mean that gasoline will get past the rings. The message only means that the O2 sensor is reading too high, and or, not fluctuating enough.

FCP has a sensor for a stick shift. I doubt your engine has an air pump.

There is a way to bench test your O2 sensor:

From Matthews Volvo site
Use a high impedence DC voltmeter. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future. There is almost always
*no* benefit in replacing an oxygen sensor that will pass the
test in the first line of this paragraph.
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Keeping it running is better than buying new