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Idle speed control on blacktop 20v 4age

Stu Jones

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Hi guys,

I'm having a bit of trouble getting idle speed controI to work nicely on a couple of blacktop 4age engines I'm currently working on.  One is running a G4 storm and the other is a G3 upgraded to G4 firmware. Both are running the stock inlet manifold with the factory 3 wire idle control solenoid and have the same symptoms.  I can get the idle up to work nicely when the engine is cold/warming up with raised idle rpm, but when the engine is hot I can't get the idle to stabilize and I'm experiencing fluctuations in the idle.  In the case of the G3 upgraded car, when it was running as a G3 the idle was fine so I have copied the idle settings over to the G4 software but can't seem to get the idle to stabilise.  Originally it was running open loop so I did try closed loop but scratching my head a bit as the idle seems to slowly increase then drop back, stumble then regain.  Any pointers?



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Hi man, 

One of the 20v 4AGEs I tuned (black top with upgraded cams etc - 1I1 off Toyspeed) had some intermittent odd idle niggles which I never actually was able to see first hand, I've come over to check it out - only to be greeted with a car which started and provide a rock solid idle at target rpm haha.  When I learnt of the extra diaphragm in the throttle assembly which contributes to the idle control (along with the IACV) we decided to stop that from playing and see if it helped, and from what I've heard it's been happy since.

Given you have loaded the exact same idle settings into the G4 Link and assuming nothing mechnically has changed, then it makes it seem like the most likely options that come to mind are:

1) The underlying tune is not the same and doesn't match what is happening

2) The new Link behaves differently - which is still probably fairly unlikely as it's meant to be pretty much the G4 firmware in an older box?!

It could well be the underlying tune, especially if you are using the same maps for both cars.  At idle you often don't want to give the car more timing than is necessary to sustain a steady idle - a bit too much and the engine can try and put on rpm as soon as it gets enough air to, it can make it a touchy situation when adjusting the airflow to try and control the idle.  From a different angle, same thing can happen if the fuel map is inconsistent.... the idle air control system would prefer to work with a consistent and fairly 'steady' engine, so make sure the fuel map is tidy and maybe dull the timing map back a bit in the idle zones (if it isn't already like that) if you feel you've tried everything else.    The fact it's fine when cold (where it's harder to hold higher idle rpm) but gets jumpy when it's warm makes it seem like it could be 'too torquey' when it's warm and idle control is haven't to shut off to stop it creeping.

The G4 Link also has an idle ignition control mode which allows the ECU to adjust timing to hold (or assist holding) a steady idle, I've managed to tune cars with no IACV at all and hold a steady idle at target rpm.

If you are keen to share your map, or even just screen shots of parts of the map you think are relevant so we can try and see if anything sticks out - that'd be helpful :)

Hopefully that gives something to ponder on!




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Thanks for your input - all has been solved.

First up I have to admit I didn't even open the engine bay and the only work I had done on it was to upgrade the G3 firmware.  I had a discussion with the owner and apparently the sporadic idle did occur with the original G3 setup after all - it must have just been a fluke with the right engine temp/witchcraft etc when he dropped the car over and the brief time I heard it running that it was ok.  On closer inspections the PCV vac line had been replaced with a section of hose that was far too soft and it was sucking in then releasing with the idle fluctuations which of course wasn't helping.  This remedied and the idle improved although still had issues.  It almost felt like a slight miss I took the plugs out and noted the gap was 0.25mm!! I re-gapped them and the idle felt alot stronger.  I few minutes mucking around with the base position table and the idle control settings and I had closed loop working perfectly.  Funny how small stuff can cause such and annoying issue.  Road tuned today and its driving very nicely.  Spent a bit of time today working on the cold start and you would swear its as good as if not better than factory cold start now.



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