VS sc V6 unstable idle issue

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vHell83
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Joined: Sun Jul 24, 2016 4:38 pm
cars: Supercharged VH V6

VS sc V6 unstable idle issue

Post by vHell83 »

Hi,

I have a VS SC V6 on e85 that currently has some idle issues. The main issue is that it won’t idle at its commanded RPM (idles at 900/1000 instead of 800) when hot and the IAC is doing 0 steps. Now when I command it at 1000 RPM it does around 35 steps but still remains idling lean in that rev range.

The engine is fresh with new gaskets everywhere, and I’ve doubled checked the gaskets in the throttle body and elbow. I have blocked off the small hole in the throttle body blade with something temporarily to see if that made any difference. After this, the car starts first go but, idles good for a second or two then the revs jump up pretty high and remains at 12.2 AFRS then as the idles come down the AFRs increase, once the idle is down the bottom and engine sounds like its choking its on 22.4.

What I want to know is, in terms of keeping a steady fat idle at all times am I better off keeping the hole in the blade or blocking it off? I know that some people tend to enlarge the hole but I’ve always been told that’s the lazy way to do it.

If I should keep the hole closed what tables should i adjust to get it going?

Vehicle mods as follow;
3.4"pulley, 450 LPH Fuel pump, 1000CC bosch injectors, stock fuel rail, intake manifold supercharger and head porting, 10:5.1 CR, LS1 TB, 4"intake pipe with LS2 style MAF, e85, mat sensor in intake manifold.
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Holden202T
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Re: VS sc V6 unstable idle issue

Post by Holden202T »

I have found with a mates L67 that lean idle was from air leaks, in his case it turned out to be a split in the brake booster diaphragm ....

the fact that its lean wont be helping idle at all .... you need to find whats causing it though, try blocking things off one at a time.

the reason its running lean is because the air bleed is not going through the MAF so its getting more air than the MAF thinks it is.... the hole in the butterfly wont matter either way as that should be metered through the MAF.

you also want to make sure there are at least a few IAC steps at warm idle, but I would work out the lean issue before you worry too much about IAC steps.

I have on big cammed motors drilled a hole in the butterfly to allow the plate to close enough so its not reading tps open at idle but still allow enough air through and to also keep the IAC steps low, but I think this is more due to having no PCV on the motor and so hense not as many air bleeds in the system.
vHell83
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Joined: Sun Jul 24, 2016 4:38 pm
cars: Supercharged VH V6

Re: VS sc V6 unstable idle issue

Post by vHell83 »

That was something else i had in mind. My brake pedal feels fantastic and the brakes respond a ton better than my other car with the same brake setup though.


The only things I havent done apart from the booster was the pcv valve and the o ring in the boost tree.
VX L67 Getrag
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Re: VS sc V6 unstable idle issue

Post by VX L67 Getrag »

With your maf so far away from throttle body it won't be helping the issues it has, but yeah make sure there's no vacuum leaks get hole in throttle blade closed & then the iac should start working if all is well then start adjusting injector multiplier table till your hitting target afr!
vHell83
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Joined: Sun Jul 24, 2016 4:38 pm
cars: Supercharged VH V6

Re: VS sc V6 unstable idle issue

Post by vHell83 »

VX L67 Getrag wrote:With your maf so far away from throttle body it won't be helping the issues it has, but yeah make sure there's no vacuum leaks get hole in throttle blade closed & then the iac should start working if all is well then start adjusting injector multiplier table till your hitting target afr!
With the hole on the tb shut the cars idle is out of control. It comes up so high then drops down to the point of almost stalling then comes up higher again and repeat.
kojab
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Re: VS sc V6 unstable idle issue

Post by kojab »

Are you running an A2A intercooler? If you are then this is whats probably causing your idle issues.
VX L67 Getrag
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Re: VS sc V6 unstable idle issue

Post by VX L67 Getrag »

Nah there's no cooler on this car.
With how far the MAF sensor is from throttle body will be giving it a delay to all fuel responses.
But once the hole is blocked in throttle the fuel will need to be adjusted as it's now not getting air it was previously & throwing fuel out & with delay it will be making it worse.
0081
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Re: VS sc V6 unstable idle issue

Post by 0081 »

How far is the maf from the throttle body that's it's causing a issue.
I just checked mine and it's 500mm away from the throttle blade give or take.

Even if it did have an A2A plate it can be made to idle. I have the A2A plate and an external water to air cooler with no idle issues.
Has about 1.3m of intercooler pipe.
vHell83
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Joined: Sun Jul 24, 2016 4:38 pm
cars: Supercharged VH V6

Re: VS sc V6 unstable idle issue

Post by vHell83 »

Exactly how is that maf position an issue? From factory the maf is a few CM closer to the TB.

Here is the idle with the hole shut.

https://youtu.be/1-Thxy3QbL8
vHell83
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Joined: Sun Jul 24, 2016 4:38 pm
cars: Supercharged VH V6

Re: VS sc V6 unstable idle issue

Post by vHell83 »

0081 wrote:How far is the maf from the throttle body that's it's causing a issue.
I just checked mine and it's 500mm away from the throttle blade give or take.

Even if it did have an A2A plate it can be made to idle. I have the A2A plate and an external water to air cooler with no idle issues.
Has about 1.3m of intercooler pipe.
My intake pipe is 50cm maybe a tad longer so my maf is actually near the stock position
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