I've got a 940 station wagon, '93 2.3L regina. I've used brickboards multiple times in the past to fix various problems that i've had but I couldn't find a quick fix on this one so I was hoping someone could give me a hand.

My car would start, idle well for maybe 35 seconds, and then start idling badly. It then lost all power when i tried to drive, sometimes stalling. I looked through the various posts and thought it might be my O2 sensor. Sure enough, when I disconnected the O2 sensor the onboard computer just compensated and the car is working fairly well. I measured output from it at a constant 45mV, which I took to mean that the sensor had stopped responding and was no longer good. I continued to drive my car and ordered a new O2 sensor through ebay. Today I hooked it up and the new sensor does the same thing. the car runs fine, I hook the unit into the wiring harness and then the engine begins to sputter and the car gets no power. I disconnect it and the problem is solved.

The idle is 200rpm higher than before and much less stable than usual, the engine sounds like it's running rougher, and I'm loosing fuel economy, or else I'd just leave it disconnected. I also read that you can damage your catalytic converter when the computer defaults to an overly rich mix.

I have some theories, like maybe the onboard computer is messing up (though it seems to run the car well enough without the sensor), or perhaps the small leak in my tailpipe about 1 ft. before the sensor is causing too little exhaust to pass by the sensor, making it report incorrectly (though again my car was running fine with said leak until a few weeks ago).

One final caveat is that the engine light was on for several weeks before the engine started acting up, so I'm not sure if the computer sensed the sensor was dying and that's why it lit up or not. Even with the new one in and after pressing the button by the clock the light stays on.

Anyone have some ideas what I might try next?

Check your codes, first. But I would advise cleaning the throttle body and the IAC. On my 1993 945 w/ regina, I had similar symptoms that were relieved by a new O2 sensor and a thorough cleaning of the IAC.
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1993 945 NA

I don't know about the original symptom, but is the ebay sensor the correct one for the Reginal FI?

The 3 leads must be Red, White, and Black.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Heh.. the ebay listing said that it was compatible with the 940, but no the leads are white, white, black.. far as I understand it though that just means that polarity is not a factor in the 12v heating unit within the O2 sensor. Is the voltage output on the sensor lead not the same on both models?

Sorry but the ebay lister is mistaken. The Bosch he sent is NOT compatible with the Regina.

It absolutely will not work correctly with the Regina FI

They both look similar on a voltmeter but not to the ECU that "reads" the sensor output in the active, i.e., "cloosed loop" operation.

You need the NTK 25002 Titania based sensor. (For tech details, Google is your friend.)

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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

If you've got a Regina car, then it appears you have the wrong sensor. See the FAQ where there is an extended discussion on this topic:

http://www.brickboard.com/FAQ/700-900/EngineSensors.htm#OxygenSensorLifeandDiagnostics

Steve, the FAQ Table of Generic repacement sensors lists the NTK 25003 for Regina 700/900 cars. The 25003 is is described as a 4-wire sensor elsewhere in this FAQ section, and as applicable only to '94 and '95 940's.

This model/year application is borne out at the NTK website , although they decribe it as a 3-wire . [However, NTK is also wrong on engine type — with no mention of the B230f, listing only the B234.]

PN 25002 is the correct PN for 700/900 Regina cars up thru 1993.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

As Bruce said, ya got the wrong one; white, white, black is Bosch.

Hi. I would advice you to check your OBD error codes. There is a well documented procedure on the FAQs, and you don't need any tools or scanner. If a sensor, such as the AMM, has failed, there will be a stored code. The button near the speedo only clears the Service Engine light, which lights up solely on mileage run, to remind drivers of periodic maintenance, such as oil changes. The Check Engine light denotes that an error code (or more than 1) is stored in the ECU, letting you know that there is something actually wrong with your engine. The FAQ also explains how to reset the CEL (check engine light) after you have found what's wrong.