Cobra running lean at idle after a WOT pull

SvtCobra0404

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i did 1st to third pull, car ran great good AFR. but the next day I started the car and usually at a cold start I have a rich AFR but this time it started with a lean AFR like 15.5-17.0 on my gauge. I drove the vehicle under no boost my short term fuel trim was 0.84 min and 1.24 max. Long term is 1.00. Could my gauge/wideband get faulty after a pull? My wideband goes through my shifter and then to the sensor.
 

01yellercobra

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Depending on the brand it might need a free air calibration. I'd look into that. If I turn the key on my wideband might jump a little as the sensor warms up, but if I don't start the car it'll go full lean in about a minute.
 

SvtCobra0404

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Depending on the brand it might need a free air calibration. I'd look into that. If I turn the key on my wideband might jump a little as the sensor warms up, but if I don't start the car it'll go full lean in about a minute.
But looking at my fuel trim, does it look like a wideband issue or something with the car?
 

01yellercobra

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I'd say it's the wideband personally. If you can datalog you can check your trims and compare them to the wideband.
 

SVTdreamin04

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Pull the wideband out, turn it on with the wideband out of the exhaust and see what it reads. Then, take a rag, wet it with gas, but don’t soak it and put it around the wideband sensor to see what it reads.

Keep in mind, the wideband does get hot, or it should, so don’t go overboard with the gas soaked rag. If the wideband doesn’t heat up, that is an issue too.


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01yellercobra

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Pull the wideband out, turn it on with the wideband out of the exhaust and see what it reads. Then, take a rag, wet it with gas, but don’t soak it and put it around the wideband sensor to see what it reads.

Keep in mind, the wideband does get hot, or it should, so don’t go overboard with the gas soaked rag. If the wideband doesn’t heat up, that is an issue too.


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I've heard of a similar test using a lighter. Don't light it, just aim the butane towards the sensor.
 

c6zhombre

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How old is the sensor? If you don't know that answer....or it's more than a couple years old....it's worth the $60 a new one costs so just go ahead and replace it. If you're going to all the trouble to "free-air" calibrate it.....just get a new one and scratch "sensor" off the list of possible gremlins.
 

jjk23

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Besides being lean at idle, car is at target idle speed?

It would be a good idea to check all of the vacuum lines on the back of the blower. I have had one occurrence where a line popped off. Car had a tough time settling in at idle and was lean.

Remember, misfires are registered as a lean condition due to the extra oxygen content in the gas stream.

Good luck!
 

SvtCobra0404

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How old is the sensor? If you don't know that answer....or it's more than a couple years old....it's worth the $60 a new one costs so just go ahead and replace it. If you're going to all the trouble to "free-air" calibrate it.....just get a new one and scratch "sensor" off the list of possible gremlins.
Sensor was installed last summer, hasn’t had much miles on it.
 

SvtCobra0404

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Besides being lean at idle, car is at target idle speed?

It would be a good idea to check all of the vacuum lines on the back of the blower. I have had one occurrence where a line popped off. Car had a tough time settling in at idle and was lean.

Remember, misfires are registered as a lean condition due to the extra oxygen content in the gas stream.

Good luck!
Scanned for DTCS and don’t have any. So doubt I have a misfire. Idle is good. No vacuum leaks.
 

SvtCobra0404

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Hello guys.

So I performed a recalibration. Disconnected the harness to sensor and went key on for 30 seconds, then removed the sensor and plugged it back in and did another key on for 30 seconds. Double checked for any exhaust leaks, all is good. Started the car back up and it’s still fluctuating from 14.7-17.0 @ idle. Idle speed is the target. Doesn’t have a vacuum leak, no exhaust leak, all the connections on the blower are okay. So would this be a bad air fuel sensor or harness?
 

Bdubbs

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I've been on a kick of replacing the sensor once a year. So far this summer mine is still working.

If I was in your situation, I'd try a new sensor. Worst case scenario you'll have a spare, and eventually you'll need it.

Sent from my Moto E (4) Plus using the svtperformance.com mobile app
 

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