Based on a few other people's threads where they are fighting start and idle issues, and the question of whether or not the O2 sensor may be contributing or even serves any purpose on our cars keeps coming up, maybe we can make a short sticky that has just the relevant info.
More experienced guys, feel free to correct this if I have anything wrong, or add anything I left out. I have an otherwise perfectly running NA with no other issues and very few variables in play, so I did some testing. It's been well-attested that turbos just don't need the O2 sensor but that wasn't as clear for NA cars.
The short version:
I can confirm that an otherwise perfectly running NA will miss and stumble a bit on a cold idle with the O2 sensor unplugged (confirmed on both 84 and 87 ECUs.) This car has no other idle controls installed (IACV, air regulator, and FPR solenoid all deleted) and idles perfectly ~750 (set at throttle body) with the O2 plugged in. Nothing changed between tests (conducted on sequential mornings), running 91 gas, outside temperature approximately 70 degrees.
Note that the car without the O2 sensor plugged in was still driveable, had no problems over about 1100RPM, and ran fine once warmed up. Repeat: if your car won't stay running without the O2 sensor plugged in, the O2 sensor is not the problem.
O2 sensor and ECU interchange information can be found here: http://www.redz31.net/pages/fuel.html. Pay special attention to this page if you or a previous owner have been swapping ECUs, or the year "1986" ever comes up in relation to your car
More experienced guys, feel free to correct this if I have anything wrong, or add anything I left out. I have an otherwise perfectly running NA with no other issues and very few variables in play, so I did some testing. It's been well-attested that turbos just don't need the O2 sensor but that wasn't as clear for NA cars.
The short version:
- If your car, NA or turbo, won't stay running without the O2 sensor plugged in, the O2 sensor is not the problem.
- Turbo cars run just fine without the O2 sensor, as the turbo fuel mappings are rich by default.
- NA cars should have a working O2 sensor, as the NA mappings are considerably leaner.
If you are having starting and idle problems on a turbo car, unplugging the O2 should not make it worse. If that happens you may have a harness problem. Best of luck with that. If the problem improves, simply leave it unplugged, and continue troubleshooting if necessary.
If you are having starting and idle problems on an NA car, the O2 sensor may be the problem. If this is the case you may not notice a difference between a bad O2 sensor and an unplugged O2 sensor. You may want to just replace the O2 sensor to eliminate it as a potential problem. - Turbo cars run just fine without the O2 sensor, as the turbo fuel mappings are rich by default.
I can confirm that an otherwise perfectly running NA will miss and stumble a bit on a cold idle with the O2 sensor unplugged (confirmed on both 84 and 87 ECUs.) This car has no other idle controls installed (IACV, air regulator, and FPR solenoid all deleted) and idles perfectly ~750 (set at throttle body) with the O2 plugged in. Nothing changed between tests (conducted on sequential mornings), running 91 gas, outside temperature approximately 70 degrees.
Note that the car without the O2 sensor plugged in was still driveable, had no problems over about 1100RPM, and ran fine once warmed up. Repeat: if your car won't stay running without the O2 sensor plugged in, the O2 sensor is not the problem.
O2 sensor and ECU interchange information can be found here: http://www.redz31.net/pages/fuel.html. Pay special attention to this page if you or a previous owner have been swapping ECUs, or the year "1986" ever comes up in relation to your car
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