G4 xtreme USDM 07 STI, Idle is over-rich sometimes over-lean sometimes....

[Eric Godden]

So here is my issue. I am using open loop e-throttle. My idle afrs tend to very widely even with the same cell being used depending on what is going on. Its rich on return to idle, its lean on warm/hot restart. I don't think my IAT sensor is causing the lean condition. I have some problems with my idle, essentially when I go to neutal or clutch-in and the car returns to idle it will idle at 12.9 ~13.9 afrs, usually starting at 12.9 and then slowly increasing to 13.9. If I turn the car off and restart it the afrs at idle will be where I have set them ~15.0afr. If I lean out the cells to remove the rich afrs then I idle very lean at other times. Another issue I am having is that if for example I drive for 20min, park, then restart the car about sitting for maybe 10min or so the car will idle very very lean 16.0 afrs +-.5, this is with the same settings as I have when the idle is rich. If I go drive the car for just a minute or two this lean condition will go away. When this is occuring the car is hot and there is usually no post start or warmup enrichment., I will start another post with these problems for neatness. Thasnks for all the help. -Eric

[Chris Conway]

I have had similar problems which I believe are caused by 'heat soak' when the engine is turned off. What I have done is to add numbers into the 'IAT Fuel Trim'so that it will increase the fuel added. I add 1% @ 30C and up to 8% at 50C at a map of 30kPa. I then reduce the % trim to 0 by MAP=80kPa. The remainder of the IAT fuel trim numbers are what would be expected for changes in air temp. ie, take fuel out on hot days and add fuel in on cold days when the engine is on boost (> 140 kPa). I have also added considerably greater numbers in the fuel cell which is generally below the idle speed. ie,850 & 1000RPM = 70 at 30kPa, 700RPM = 78 @ 30kPa. This also seems to help maintain stable idle. I also used open loop idle speed control and fix the idle air valve position rather than using closed loop control.

[Eric Godden]

Thanks for the input I will give them a try and report back

[Peter Giljevic]

In my own cars case I make use of the fuel temperature sensor in the fuel rail as it is super fussy with regard to idle AFR setting and it needs to be constantly within 0.5AFR in every operating condition. Fuel temperature (and thus density) will vary allot from overnight ambient temp to 50 deg C when running and go as hot as 90 deg C or more on a heat soaked engine, Every 10 deg C in fuel temp you really need another 1 to 2% more fuel as the density changes *gets less with more heat*. This is why this problem is never fully cured by AIT figures because as soon as the fuel circulates and the rail, reg and injectors cool after a minute of running all of a sudden the fuel mixture changes allot at idle while the intake manifold is at the same temp basically. In my car the AFR is within above band from hot shut down to 20 min heat soak restart and operating the engine from 37 deg Ambient to 5 deg C cold start. I have my fuel temp map compensation set up under one of the tables (RPM to FUEL TEMP) and it works well, only way to fully solve the issue you are having.

[Chris Conway]

Superb, I will give this a go. I assume that a water temp sensor would be suitable?

[Guest Dave]

alot of factory cars have fuel temp  some are done at the tank not at the rail though as well as fuel tank pressure      

the main factor with factory cars are the time spent on the base tune   running a airflow meter and then let closed loop lambda and short and long term fuel trims correct as needed

Regards

David Heerdegen

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