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Warm start - irregular idle


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I recently purchased a 2000 gc8 wrx with Link G4+ ECU.

On occasion, warm start gives a rising and falling idle. Cold start is fine.

Usually I can just turn it off and then start up again and it's fine. Today it happened and wouldn't start back up. I left it for a few minutes and then was ok.

I had enabled PC logging for >500rpm so I captured the issue and have attached the log along with the tune file.

Are you able to have a look and let me know if there is something I can do?

This is my first car with aftermarket ECU so I am not familiar with the tuning process.

Let me know if you need anything else for diagnostics.


Warm start_irregular idle.pclr Warm start_Irregular Idle_Log.llg

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The really short answer is you are having overrun fuel cut kick in, which is causing the rpm to drop every couple seconds. This is happening because your idle RPM is so high that the ECU thinks that you are coasting to a stop. When it drops below ~1800rpm in your config its not allowed to cut fuel (so you dont stall rolling up to a stop sign), and it turns the injectors back on, pushing RPM back up.

How to fix it... 

When its idling normally, does it idle this high or more like ~850rpm like it says its configured to? Can you post another log of it idling normally as I suspect it is leaning really heavily on the close loop adjustments.

You need to get the idle down enough so that the ECU actually considers it "at idle" and the idle control systems kick on. idling at 1700rpm you are about 600rpm above this point and so most the corrections to hold an idle RPM of 850 arent even applied.

you could try increasing the "warm" numbers in your base idle table (higher numbers = lower idle on stepper motors normally).

If that doesnt help you could run through the idle setup process by swapping it back to open loop, running it through a warm up cycle while adjusting the base idle numbers at each temperatue point, then swap back to closed loop once open loop is behaving well. 

There are also things you can do with idle ignition to make idle more stable, but you need to get the idle within ballpark first or it will have the same problem of not kicking in at all if your RPM is this far above target.


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Thanks for your prompt reply.

Yes, normally it idles ok at 850

I logged another drive last night but the file size was over 10mb so I couldn't attach it. I will log a drive this morning of idle normal and upload.

One thing I forgot to mention, usually it does take a few seconds to start once warm. when it does it's low revving but comes up to idle (850) after a second or 2.

When comparing yesterdays and todays logs, the 'IAT Fuel Corr.' value is noticeably different at -3.5% right from engine start. This was about the only difference I could see when it does rev up and down compared to starting and idling normal.

"you could try increasing the "warm" numbers in your base idle table (higher numbers = lower idle on stepper motors normally)."    -     I've only clicked my way through logging and reviewing data so far with that being the extent of my knowledge and capability.... Can you guide me in changing these numbers?



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The highlighted cells below are the base idle position at a given coolant temp. The cell from 70-100 ish are normal operating temp. You can see in your last log that your coolant temp @ startup was 83deg C so the 80 & 90 cells would be interpolated for this. Try adding 10-20 points to these values and try again. This isnt a 1 step fix, but is a good way to check if we are on the right track - ie we should see some improvement.

This is the table you will re-build/re-check in open loop mode (change in "idle speed control") if we cant fix it with small tweaks. 


FYI you can upload files to google drive/dropbox/onedrive and link them here if the logs are too big.


The slow start when warm issue might be the IAT trim you mentioned. Try zeroing out the hot 0% tps cells highlighted below, or maybe even change the 50+ cells (just in the 0% row) to + 3-5%. Heat soak will cause the IAT to read really high which can cause insufficent fuel for warm start. This is likely not the cause of your high idle though.


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Ok, so I've changed the warm idle values and will see how it goes.

Being an intermittent problem it may be a while until it occurs again.

Attached is a log taken just now, cold start idling to operating temp.

And the link below is for the log taken yesterday showing idle and re-starts ok.



Cold to warm idle.llg

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that normal warmup log shows that after closed loop idle does its thing, the resulting idle positions at the various temps were:

20 30 40 50 60 70 80
188 198 206 210 216 225 228


You should put these values into the base table and then interpolate up from there - which is pretty flat anyway so 90+ should probably all be 230-235 ish. This will mean closed loop is doing a whole lot less real-time modification to the idle table, and the open loop values that are used before CL can kick in will be much closer to the idle you want. 

Using these plus the IAT fuel trim changes should help.

If idle is still bit unstable try turning on ignition idle control, and if it still hangs just above 1200rpm when it should be idling, try bumping up the "RPM lockout" in idle speed control menu to 500.

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When I use those values for my idle base, it won't start. I tried a few times and also with a little throttle during cranking but the revs just fall and it stalls straight away.

Log: https://1drv.ms/u/s!Ah20vN2_b-_wiNp5qm1gaAiU1wAK0Q?e=dZIHxj

I changed back to the previous idle base and entered the IAT TP0 fuel trim to 0 for >30deg and then logged cold start idle until warm then revved over 2500.

Log: https://1drv.ms/u/s!Ah20vN2_b-_wiNp7ICBI_F5ghQMG7g?e=JS2nJw

I'm gonna go for a drive shortly and can see how it goes.

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Only thing I can think of is because its a stepper motor you need to power cycle the whole car after changing settings as the whole system is based on "X steps from start position" The big assumption here is that start position is always 0.

Looking at your log where you said it idled low, weirdly the idle position is 222 @ just under 900rpm with coolant at 87ish and mid 20's IAT. this is quite a ways from the ~230 steps it was showing on your previous log. I wonder if your stepper isnt fully resetting at key off. your hold power value is 0 seconds, try setting it to 3 or 4 seconds and see if things become more consistent.

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Reading through this my thoughts are that for it to idle that high (and it seems to be wanting to idle even higher but was limited by overrun fuelcut) it has to get a descent amount of air in to it. So im thinking sticking or incorrect stepper control.


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I nearly ordered a new one this morning but thought I'd see how the upper engine cleaner went.

I accidently turned off the laptop on the drive northside so only have the return trip data.

Log from this afternoon: https://1drv.ms/u/s!Ah20vN2_b-_wiNwVFQLauIvBOI0fuw?e=9SPo7i

Cold start, idle and warm start were all good.

I'll go ahead and order the IACV as it all seems to be pointing toward that being the issue. I found one in Perth from online supplier Auto Sensors for $60. (not sure if that's too cheap as guys from other forums have said they were 300 and up)

Also, to clean the stepper motor, I warmed the engine then turned it off. Removed the unit and sprayed upper engine cleaner into the base of the valve until it wasn't coming out dirty anymore. Reconnected the plug and turned the ignition on so the valve moved all the way out and then sprayed it again until the rest of the dirt was gone. Let it dry for a few minutes then reinstalled. Build up didn't seem too bad but I'm not sure how much it takes to affect its normal function. And I as wondering should I spray the rest of the can through one of the vacuum lines into the inlet..? I read that from the back of the can. It seems to be running nicely at the moment so I don't want to introduce any new problems if it's not usual practice.

With a new IACV, does the idle base need to be logged and adjusted to suit the values of the new unit?

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Don't buy a $60 IACV.  Been there done that for research purpose. It did not fit as advertised and when I started fiddling about with it, it flew apart in my hands.

Do you have a wideband on the car? It is not picking up in the logs. CLL corr is up to -4% at idle.

Don't be to quick to blame the IACV. The best thing you can do is retune the whole thing in open loop using the base position table. The Link help files are quite comprehensive covering this. 


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Thanks for the heads up regarding the idle control valve. I'll hold off until we're a little more sure.

No wideband.

The rising and falling idle at warm start occurs few and far between. I was thinking I want to see how these few adjustments go before adjusting idle any further.

Do I need to retune the idle even though the idle is good.. This only occurs on the 1-off and I can usually just shut it down and restart?

I'll give it a few days and see if I can replicate the issue.


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