2000 Corolla Lean Fuel Trims After Replacing MAF

  • Bernard_s3
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2 months 3 weeks ago #201284 by Bernard_s3
I replaced the MAF on my 2000 Corolla with a new Denso MAF and now fuel trims are lean (fuel trims were within spec before replacing the MAF). LTFT at idle is pegging at 19.5, sometimes it comes down to 17. STFT at idle varies from 3-12. LTFT comes down quiet a bit to around 11% while driving, where STFT fluctuates -3 to 8%. I checked to make sure the MAF was seated correctly and it does have the o-ring. I am not throwing any trouble codes. I have not re-installed the old MAF, although I will since it's possible the new MAF is defective - but would that drive the fuel trims that high?

The previous owner of this car threw a lot of parts at it to try to remedy a misfire - one of those parts was a Dorman MAF. I have been having some slight hesitation around 1/3 throttle @ low RPMS. I figured I'd go ahead and replace the cheap part with a factory part and start there.

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  • nightflyr
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2 months 3 weeks ago #201285 by nightflyr
Replied by nightflyr on topic 2000 Corolla Lean Fuel Trims After Replacing MAF
First thought would be a ECM reset ( disconnect the negative cable from the battery over night ) then take a long drive so that the ECM can relearn its fuel mapping.

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2 months 3 weeks ago #201287 by Bernard_s3
Replied by Bernard_s3 on topic 2000 Corolla Lean Fuel Trims After Replacing MAF
Overnight? I though five minutes would suffice, which is what I did.

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2 months 3 weeks ago #201288 by nightflyr
Replied by nightflyr on topic 2000 Corolla Lean Fuel Trims After Replacing MAF
5 minutes ....
Depends on the vehicle, perhaps if you completely discharge the system by grounding the positive cable.

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2 months 3 weeks ago #201301 by relative4
Replied by relative4 on topic 2000 Corolla Lean Fuel Trims After Replacing MAF
Smoke test
Make sure you got the right Denso part number

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