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WH Statesman 3.8Ltr 6 cyl with a Dangerous issue

VFSV6FORME

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My son's Statesman 6 cylinder with a 3.8 litre engine has an issue which I classify as dangerous and for the love of money I cannot find out what is causing it. I have spoken of this in my other thread about my son's Statesman but this deserves another thread by itself.

The issue is when the car is cold or the car has done only half a km from home the idle in neutral or in park after you put it in these two positions because you feel the car wants to go on, the idle goes up from 1200 or even up to 2500 rpm, yes you pick this whilst driving the car as you come to a set of lights, you put the foot on the brakes and the car wants to still go forward, so you put it in park or neutral and up the revs go from 1200 to 2500 rpm.

Now, I have spoken about a sticky throttle, but its not that because the car drove in my driveway and it was doing 2200 rpm in park so I lifted the bonnet, grabbed the throttle cable on the throttle body itself and slammed it shut, which it was shut, it was 100% shut. I grabbed the cable again and opened the throttle body more and slammed it shut again, I heard the thud sound, so it was 100% shut, but still the car was idling at 2200 rpm, so after this I suspect that either the idle control valve was getting a fake message from the ECU that was making the car idle that fast or was that EGR valve, I think its the EGR valve, that motorized unit that sucks exhaust gases ( from the Passengers side exhaust) , goes through this motor and then injects it on the manifold side of the throttle body.

Now, this exhaust gas to the manifold if they call it the EGR valve that looks like a windscreen wiper motor, I have blocked that now to test, but it still does it, but I will go back on the last paragraph when the car was idling on 2200 rpm. To get it to go back to normal, forget about slamming the throttle body , forget about the EGR valve, most of the time, I say most of the time, turn the engine off, then start it after a minute and the car idles on 900 rpm.

Now, it only leaves the Idle control valve and since I have changed two of these I don't think its the idle control valve that is causing the issue not unless it getting a FAKE message from the ECU. Now, I got my spare idle control valve and I wound it in so it allows more air flow in, I put it in the car, did not connect it and started the car and the car revved about 2700 rpm, so by this, you can see that the idle control valve can allow this car to idle at 2700 rpm in park or neutral, so the question is if the idle control valve is causing the issue, what can cause the idle control valve to fully or partly wind in (more air come in) that allows too much air in that makes the engine idle from anything from 1200 to 2800 rpm?

What else could cause this? Does this car have an intermittent power booster issue that is allowing vacuum in the manifold that allows the car to have a higher RPM when the throttle is fully closed? Or what do you think about that other valve (forgot what its called) the one that sucks the fumes from the petrol tank then goes through a solinoid and after this goes to the manifold side of the throttle body. So what happens if this is stuck occasionally open?

This issue with this Statesman has confused me because its not my car, otherwise I would have changed everything with a new throttle body, new EGR valve and new everything else, but I have a feeling if I did this the problem would still be there, something is occasionally allowing air to come into the manifold to make it idle to 1200 to 2800 rpm and as soon as you turn the ignition off or turn the ignition off again and wait for 5 minutes then turn the car back on its OK, it idles on its correct RPM, which is about 900 rpm.
Once again its not a stuck throttle cable, its not a Cruise control cable as its disconnected so what do you think I have missed.
 
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greenacc

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Try completely plugging the IAC port with something eg a piece of dowel. Another possibility could be air leaking past a gasket somewhere around the intake manifold but that doesn't usually make it rev so hard as there will be excess air with no fuel.
What about The TPS ? When they get old they variable resistor inside it sends dodgy values to the computer because it misreads the actual throttle position due to the error in resistance.
 

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Air intake pipe after the MAF not sucking in air? Plenum gasket down tight? Throttle body housing sealed? O2 sensor MAF TPS and IAC work together as one, I don't think your EGR be the issue Your engine will run rough at idle and stall, If yours is running high and the butterfly is closed in the body throttle then your IAC is allowing more air in leaning the mixture, if you don't have any leaks around your intake then it only leaves 4 variables which is telling your computer to allow more air mixture via your IAC valve.

Is it throwing any fault codes?

Oh I forgot to say even a damaged fuel Injector can cause a lean mix. Pull the plug out if the plug is light in color it would mean that injector is damaged.

 
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VFSV6FORME

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Try completely plugging the IAC port with something eg a piece of dowel. Another possibility could be air leaking past a gasket somewhere around the intake manifold but that doesn't usually make it rev so hard as there will be excess air with no fuel.
What about The TPS ? When they get old they variable resistor inside it sends dodgy values to the computer because it misreads the actual throttle position due to the error in resistance.
What I'm doing today when the car arrives later on the day I will put the Spare Idle control valve in, make sure the car idles at the correct Idle speed which is around 850 RPM and then remove the wiring harness (hope this does not cause other issue) and since its left with the correct idle as it stuck there with no power feeding it lets see what happens as the car will be left at my place to start it morning and arvo.

The TPS is NEW and I have checked it with the Multi Meter as the Ramp voltage is from 0.5 V at fully shut to 4.5V fully open. Yes tested it goin up and down and all is ok with no flat spots.
Now if I have a broken pipe, hole in a rubber somewhere why does it fix it self by itself sometimes and run ok for at least 4 to 6 days until it stuff up again.

If I had the fault 24/7 (high RPM from 1200 to 2700 RPM) you would find the fault but its a intermittent one and plays up when the car feel like it.
 

VFSV6FORME

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Air intake pipe after the MAF not sucking in air? Plenum gasket down tight? Throttle body housing sealed? O2 sensor MAF TPS and IAC work together as one, I don't think your EGR be the issue Your engine will run rough at idle and stall, If yours is running high and the butterfly is closed in the body throttle then your IAC is allowing more air in leaning the mixture, if you don't have any leaks around your intake then it only leaves 4 variables which is telling your computer to allow more air mixture via your IAC valve.

Is it throwing any fault codes?

Oh I forgot to say even a damaged fuel Injector can cause a lean mix. Pull the plug out if the plug is light in color it would mean that injector is damaged.

But why does the car choose when to play up. Remember this car has a new LIM gasket fitted

ASAIK the car is spitting no codes but will read again when the car come back to our house this morning if the car gets here.

but if having a damaged injector will it cause it to go to 1200 to 2400 RPM Hummmm Running out of suggesting as to why this car is doing this. My gut feeling the Idle Control valve is opening up full bore or half open by a stray message from the ECU.
 

VFSV6FORME

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Sounds like it’s sucking air from elsewhere.
sound like it but this one fixes itself when it suit it. know if I have a hole somewhere the hole will stay there and not fix itself up.
 

greenacc

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sound like it but this one fixes itself when it suit it. know if I have a hole somewhere the hole will stay there and not fix itself up.
Unlikely but never be too quick to eliminate any possibilities. I've seen some very smart people get fooled by the simplest problems on occasion.
Back on the IAC valve, they really don't like being played with or the pin pushed or pulled in and out. I did that once and had to get a mate with a tech2 to reset it for me.
Now I heard a rumour some years ago that might help. Don't know if it's true or false.
Apparently when you turn the ignition on the IAC valve advances. So if you have a fast idle problem caused by the bin allowing too much air in, they claim you turn ignition to on then disconnect the IAC.
Then turn ignition off, reconnect IAC and turn ignition on again. Repeating this process slowly advances the needle until it's home. Might be true but I thought the pin would open up for cold start and not close so don't know what the deal is...
 

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Try another PCM.

Oh I forgot to say even a damaged fuel Injector can cause a lean mix. Pull the plug out if the plug is light in color it would mean that injector is damaged.

That pic may be true for an old carburated engine however with modern EFI plugs will still come out looking clean/lean because of the lean cruise function.
 
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