Lean idle on Aristo 2jz

[CSquared]

Ok so I am an Aristo 2jzgte swap single turbo… I am trying to tune the car with a SAFC NEO and Autometer wideband. I understand that I cannot tune below 4000-ish rpm due to the ECU being in a closed loop. However, my air/fuel ratio at idle is currently bouncing around between 15.5 and 16.0 (but the idle will stay flat) when it should be somewhere closer to the 14.7 area from what I understand... and it stays in that general area during normal driving... I haven't made boost yet for fear of detonation.

Here is my car:
-Aristo JDM ECU/MAP sensor
-SAFC NEO
-Precision T67 DBB turbo
-Autometer wideband
-Injectors (stock 550cc) were professionally cleaned and flow tested within the last year
-Fuel pump (stock denso with 12v) and filter are both brand new
-All wiring (including safc) was done by tweaked performance (phoenix tuning)
-Ratio remains the same even when the car is fully heated
-Car is OBDI

I am guessing my next step will be the O2 sensor but I am hoping to get some suggestions as the O2 is freaken 100 bucks and I don’t want to sit here replacing parts until I find the culprit (I’ve seen more than a few threads where they replace te sensor with no change). The only thing I can think offhand would be the downpipe which is currently cut about 12-14 inches below the O2 but I am skeptical about that. I would think that the leak would need to be before the O2… I rechecked torque on the exhaust manifold and even tried to readjust the v-band from the turbo to the downpipe. I'd just like to get the car to a point where I can drive it to and from the shop that will be doing the rest of the exhaust.

 

[Dirgle]

That's where my aristo with stock twins on factory ECU idles. No issues here, as soon as I start to go positive on the pressure side I shoot straight toward 11.0.

 

[CSquared]

Really? Seems like every post in the world about idle air/fuel says it should be in the 14-15 range. Sadly I'm trying to work through this tuning bs but I truly have no idea what I'm doing and this is a crappy way to learn. Are you using any sort of fuel control or is that on a totally stock setup?

 

[Dirgle]

16 is rather typical with modern engines. On my friends EVO X I've seen 17-18 AFR at idle. From what I read it's the 7M that doesn't like to idle if you get past 15:1 AFR.

It's on a totally stock setup. I managed to make 260 RWHP in stock trim and boost levels.

edit:
The important thing is that once the engine starts to see a load it brings the duty cycle of the injectors up and enrichens the mixture.

 

[OneJArpus]

i'm seeing 19=25 @ idle, but came to the conclusion that the welder i used might of not did a good job. So i'm moving my wideband back up top where it was before when i was getting a reading of 11-16

 

[gurley0916]

I see 16-18's at idle and i have stock ecu and stock fuel with the same turbo as you. Its normal

 

[CSquared]

Ok good to hear. I actually drove the car around a few miles today and the AFR stayed consistently 15.4-16.7 under normal driving and seems like it came down a bit on idle staying more so in the 15's (I guess the ecu self-adjusting). I got into boost a little bit (prob 3-4lbs) and the AFRS were high (say 12-13ish) which I really won't have a chance to play with as the car is currently not registered or insured and I am stuck more or less on my block as a result.

*But my new big question is this... I noticed a lean spike after revving the engine, in between shifts, and when going into neutral to say stop at a light or stop sign. I mean it pegs my gauge at 20 in those instances. I imagine the spikes might be normal as the engine is idling down but is this actually normal? Are you guys getting anything similar in those situations?

 

[Dirgle]

Yep it's normal. Above 1500 RPM if you let off the throttle the ECU cuts the injectors, probably as a fuel saving measure. Your ARF gauge just can't go past 20, so that's what it shows when there is no fuel.

 

[honeydew]

That decel spike number is normal. That's interesting about the AFR at idle on these engines, I did not know that. I don't know how open you are to my backyard suggestions but what might help when tuning in such a confined area is brake boosting. You can build the boost while not needing as much room, and clean corrosion off your unused brakes. I'm certainly not suggesting to break the law by speeding or driving on roads where you need a licence.... can't stress that enough. (covering my butt. *Oh hi! big brother, didn't see you there.*)

 

[CSquared]

Awesome. Thanks again to everyone for easing my mind. This car sat in a backyard basically for the last year and a half and I've dropped so much damn money that I'm paranoid at this point to blow it up again (7m rod knock on basically stock damn setup).

Honeydew... lol I have a license. It's the car that's illegal as hell at the moment. I might have to try that though as far as the brake boosting. I am insuring it as of today though to at least half please big brother.

 

[CSquared]

Ok so the car was running great last weekend... I came back this weekend, started and now it is stumbling all over itself with my Wideband pegged at 10 (it doesn't go any lower than 10). I adjusted the safc until it was about 14.7-15 and had to pull out 40-50%... which the damn 550's are not 50% bigger than 440.

Nothing has been changed since the last start... O2 sensor?