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Low Idle BS

Davo_vx

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Hi Lads after some thoughts on where to go next because I am spent. I've got a vx v6 almost every time I pull up at the lights the idle will drop to almost stall then come up but vibrates when stopped and the vibrations are giving me the shits. doesnt normally do it till its warm, same deal putting into drive or reverse when its warm. I've just recently noticed also if i am in drive turn the fan onto its highest setting the idle drops as well. I've cleaned the TB, switched out I.a.c and tps, changed cam angle, no vac leaks at rear of plenum or anywhere else I can see, purge hose is all good, new plugs, new fuel filter, intake manifold replaced, leads are less than a year old, tested coil packs all good. cleaned maf, engine mounts are all good. Just want to add fire sometimes and say are you happy now lol. On a side note the drivers window plays up every now and then only the drivers though wont go up or down and the relay will click loudly but dont think it could be related to idle issue?
 

immortality

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Have you tried a new DFI module? Coils do age and I'm not sure if a simple resistance check is sufficient as it uses a low voltage/current (from the meter) when under running conditions (high voltage) it may behave differently.
 

Davo_vx

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I haven't replaced the dfi module yet I might do that and see if it makes a difference. Any thoughts on why when turn the fan to high in drive the idle drops to almost stall?
 

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A high electrical load (aircon fans) will result in the alternator working harder to provide the needed juice which puts a load on the engine via the serpentine belt...

In some designs, the aircon is cut when an engine approaches idle speed or engine is idling and the power steering pump is under load (when parking). Such is usually done on small engines with small batteries and primarily to reduce load and potential stall at idle.

This should not be an issue for a big 6 as no need for such systems but note that Holdens are voltage sensitive... So if you’ve looked at everything else, check the alternator as it may not be charging the battery correctly and as such voltage may drop a little too much under electrical load. Things like ECU/BCM may not work well without correct voltage being fed to them.
 

Davo_vx

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Funny you should say that because I had advanced engine diagnostics hooked up yesterday looking at the voltage and the battery volts would drop from charging at 13.6 down to about 12.8 when turning that fan on in drive, no ac button onjust the fan and headlights, is that voltage to low?
 

Davo_vx

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I should also mention that I have no trouble with engine power, I do alot of highway driving and it picks up great, its only when i pull up she goes to stall and idles low and vibrates like a mofo.
 

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Also when I bought this one about a year ago the bloke said he'd had the aircon recently worked on don't know if aircon can cause idle issues?
 

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Idle control compensates for accessory load. When the thermo fans come on it automatically increases the number of steps it opens, same for the AC system so that it maintains the desired idle rpm.

Has the idle stop screw ever been played with?

A tired alternator will also cause similar issues, I know our VX had totally worn out brushes in the alternator after 210,000km. In my case it was bad enough that the battery light would sometimes come on. I put a new alternator in the sucker and got back to a nice healthy 14 volts at idle even with load (AC and headlights on etc).
 

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Dont think the stop screw has been messed with looks all good, I think I'll start with the alternator and see if that makes a difference. Then work my way back to dfi if not. Will let you know how it goes. Might get time later tonight if not will do sometime over the next couple of days.
 

Davo_vx

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Ok so I changed the alternator brought the volts back to 14 and 13.8 under load so that's good now but still same issue, I changed dfi, coil packs and igniton leads just to be sure and it seems to be idling a little better but I think the problems still there will know for sure tomorrow when I take it for a decent run.
 
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