idle slowly goes full lean


high on gas fumes
Sep 21, 2003
I've got an issue I can't figure out. After idling for a few minutes, the AFR will slowly go lean until it reaches -- on the AEM gauge and is showing 18.5 in the PL. Fuel pressure isn't dropping when it does this, and I've adjusted the IAC and TPS to read where they should. There's a MAF translator with an unknown MAF, but the previous owner set the base switch to "85mm sensor" . Also, the o2 sensor was replaced recently. Just got the PL installed on this car(newly purchased) so I'm trying to sort out all the problems the car came with. Here's an idle log with a couple revs. Thanks.


  • idle.dat
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I tried the MAF from the other GN(which has no issues) and it it didn't make a difference. Also tried different settings in the translator to no avail.
I think it may be a faulty WBo2 sensor. When the gauge reads full lean, I unplugged the sensor, plugged it back in and find that the gauge goes back to reading in the 14s. Then after another short period, it slowly goes back to reading lean. Rinse and repeat unplugging and plugging it back in and it goes back to reading in the 14 range. So, I guess I got a bad sensor since this AEM WB kit is brand new. Also, while all this is going on, the o2 volts remain the same. If it were really going lean, I'd imagine that the o2 volts would drop, right? Or atleast they'd fluctuate. Anyway I'm going to get a new Bosch 4.9 sensor and see if that cures it.
You should expect the stock O2 and wideband to basically agree.

At 18:1 the stock O2 will be very close to 0 (as you said)

Also, at 18:1, then engine will not run (or maybe just barely).

Post back what you find.

1. Determine the MAF that is in it...or the one you're going to use
2. Used a Denso 02 sensor.
3. Determine the chip you're using.
4. Here's the instructions for the Translator for all the settings...