AFR reading lean at Idle and 'normal' driving Options

[Soulend]

Hey everyone,

I am trying to find out why my afr has started to lean out during idle and normal driving. when under boost and load it will rich completely to 10 and --- green (under ten) but if I let it idle it will lean out to 17.9 then stay at --- red (total lean reading)

when I had replaced the oil and water pumps, and after re-timing I got perfect 14-15 ratio. but since then (April) it started to lean out and slowly drop since early august. I also even get a little hiccup when the car gets into low rpms and at idle.


and thing I should look at to try and fix it?

Thanks everyone,

Kevin

[Smaay]

what engine? if its a MAF car you have a vacuum leak. if its a MAP car then its another, however i have no idea what it could be without seeing the car. its possible your fuel pump is falling off, injectors are dirty, your O2 sensors is bad. speaking of which, what sensor are you using

[Special_Edy]

Like smaay said, a vacuum leak, defective MAF or MAP(the mafs are real finicky) a bad O2 sensor or a bad AFR meter.
If you hook a diagnostic scanner to the OBDII port, supposing you have one, you can read the long term and short term fuel trim as well as the MAF/MAP readings

[Soulend]

Thanks Guys,
it's a 3rd Gen 3S-GTE.
I have a less than a year old Walbro, not sure about the injectors, and I am using an AEM UEGO which is also less than a year old. now I know its still possible they are going bad, just saying that because its lessens that fact.

so I guess its MAP. kinda hoping for vac leaks...

[delusionz]

stock ecu? what happens if you unhook the battery to reset the ecu?

[lagos]

Do a boost leak test and check for any cracks in your exhaust.

[Syaoran]

Kinda weird but it sounds like your gauge is acting as a narrowband gauge would... (rich under boost which is below 14 for those gauges, and lean while at idle, which is anything above 14.7)

[bsamps4]

My car has a similar symptom. It will start acting fine after a few minutes of driving though. I'll have to admit it is pretty scary. I've never seen mine go as lean as 17 though. Maybe your IACV is acting up?

[bsamps4]

BUMP on this I want an answer

[soulshadow]

Narrow band O2 sensor or wideband?
If your still running on Narrow band its tough to figure out exactly what number your at since its either rich or lean.

[Soulend]

its an AEM UEGO wideband. a friend of mine said its normal, but I have a feeling its not. not after a few months of it running around 15, then suddenly dropping.

[lagos]

its an AEM UEGO wideband. a friend of mine said its normal, but I have a feeling its not. not after a few months of it running around 15, then suddenly dropping.

Its possible that the sensor needs to be replaced. I've replaced mine a few times over the years.
When it starts to go bad, youll notice that the gauge will not read richer than 14.7 under boost.

so go see how it behaves under boost. It should go into the 10s or 11s if its working correctly.
You can get the replacement sensors online for about 50bucks.

This post has been edited by lagos: Sep 20, 2012 - 3:22 PM

[delusionz]

changed your fuel filter?

[soulshadow]

A leaking exhaust will cause it to lean out too!

[bsamps4]

I smoke tested my car the other day and found a few obvous leaks. Had those fixed, and the condition improved. Still run a tad lean for a few minutes after hot starting from time to time, but it seems like that was the error in my case. I'm running the factory o2 sensor, and use an innovate wideband in addition to monitor my fueling. I hit super low 10's above 4000rpms at max boost, so the sensor is good to go.