Implications of a Lambda sensor disconnected by PO

[bruscreen]

While working on my brakes last year, I noticed a mysterious pair of wires hanging in the driver's rear wheel well. At the time, I dismissed it as part of the non-working power antenna. I pulled the wheels again last night for a bearing replacement, and paused to trace the wire - to the Lambda sensor. The end of the wire has been covered in electrical tape and left disconnected by a previous owner.

Before I go re-connecting the sensor, I'd like to know if there could be a good reason for it's being disconnected, and if so, are there other modifications that would have been made at the same time that I should look for? I should probably mention that the engine starts and runs well from what I can tell, though I haven't driven it very much yet (maybe 250 miles since I've owned it).

If the sensor should be re-connected, I don't have a "matching" wire to connect to - the sensor wire is thin and black, and the other loose wire coming from the cabin is thick and blue. Could that be the right place to plug in to?

[Exolis]

My O2 Sensor wire is black and the wire it connects to is blue, so based on your description, it sounds accurate.

I notice idling will be a bit different with it disconnected. Mine kinda hunts a bit with it connected while warming up, then when the engine is warm it will idle 1k+ with it disconnected and around 800 connected. So basically depending on if that O2 Sensor is working, it will have a voltage when it's warm.

Connecting and disconnecting this while the engine is running will cause no damage to the vehicle. I'm not sure how it reacts while driving if you were to connect or disconnect it, but while idling, you will see different RPMs.

[Patrick C]

If your car was tuned to run "open loop" as many DeLoreans are, plugging in the sensor could throw things off a bit in terms of the mixture. Open loop yields the most power, so if the engine is running well, I would probably leave the oxygen sensor unplugged. My $0.02

[David T]

Very likely things were adjusted to make the motor run without the O2 sensor. Hooking it back up will require readusting things to make it run right.
David Teitelbaum

[bruscreen]

Thanks guys! Sounds like this is something I can experiment with when the serious issues calm down (bearings, brakes, AC etc..) For now, as long as it's not a big problem, I think I'll just find some way of tying the wires up to the frame to so they don't knock around so much, and call it good.

[DMC5180]

I've heard of the CO mixture being dialed in with the O2 Censor plugged-in then Disconnected. It gets rid of the infamous Lambda system induced Idle hunt.