Rough idle - what could it be.

[VECom]

Hi guys,

I'm got a problem with my VE (2006) Commodore and was hoping someone here might have some ideas or suggestions on how to fix it.

It's got a rough idle and has been so for quite some time and it hasn't got any better or worse. When it's cold it idles up an feels good but after 5 or 10 min and the 'choke' is turned off it drops down to 600rpm and it's a very rough idle. It's never stalled and is very steady but shakes the whole car like its on 4 or 5 cylinders.

I've also noticed if I'm cruising along at about 70kmhr with the engine lightly loaded and about 1250rpm in top gear it's a bit jerky.

When I start the car up it says 'System check ok' I had a friend who had access to a diagnostic tool and we plugged it in there were no faults in either the engine or gearbox ecu's. We also used it to individually cut each cylinder and they all seemed to have the same effct. i.e. they all appeared to be firing.

I've replaced the spark plugs and checked the inlet manifold 'o' rings and elsewhere for air leaks but it all looks ok.

I'm a mechanic so I'd like to fix it myself but not in the industry anymore so no longer have access to a workshop or diagnostic equipment. Replacing parts isn't a problem but what do I replace? Blocked injector, air leak, a sensor?

Any help would be appreciated,

Greg

[mr031]

sounds like coils

[VECom]

Could well be. So can I test them or is some special test unit needed?

[Gorrell72]

Sounds like big lumpy cams

[VECom]

Feels like big lumpy cams Just a pity it doesn't go like big lumpy cams.

[VECom]

So anyone know how to test the coils?

[cunno]

multimeter, check resistance across 2 terminals on each pack and see if their is any big difference between the 3

[shane_3800]

multimeter, check resistance across 2 terminals on each pack and see if their is any big difference between the 3

ve alloytecs have 6 coils

[Craig93]

Sounds similar to what my car is like.
Ive been told possibly fuel filter issue or oxygen sensors from what i have asked about mine.

[LittleMissVE]

ve alloytecs have 6 coils

I don't actually understand what you're all talking about... But from the gist of what I've just read.. 2x3 = 6.

[VECom]

VE has 6x1=6

Each cylinder has a coil direct on top of the spark plug. Nice design but you can't get the coil off or change the spark plugs without taking the inlet manifold off first. I could test the coils if I had a factory spec to measure them to.

Fuel filter I would think would be noticeable under load not idle but I could be wrong.

O2 possibly. Are these in service on idle?

Craig I've been ignoring it for many months but I've finally conceeded to the fact that it's not going to fix itself so decided to make a bit more of an effort.

Greg

[shane_3800]

I don't actually understand what you're all talking about... But from the gist of what I've just read.. 2x3 = 6.

the two times three setup on the vn-vy v6's is a dfi direct fire ignition there are 3 coils that earth to them selfs so two sprak plugs fire at once it is also knowen as waste spark

[TraidMarc]

Sounds like big lumpy cams

I was going to say, maybe someone gave you a cam job!!!!

[LittleMissVE]

Well.. At least my maths was right if nothing else!

[gsh1970]

Dirty air filter? If your fuel consumption is up that may point to air filter

[xoom]

hmm my car idles at 550ish when its warmed up.

its my first v8, thought they all idled low?

[Craig93]

VE has 6x1=6

Each cylinder has a coil direct on top of the spark plug. Nice design but you can't get the coil off or change the spark plugs without taking the inlet manifold off first. I could test the coils if I had a factory spec to measure them to.

Fuel filter I would think would be noticeable under load not idle but I could be wrong.

O2 possibly. Are these in service on idle?

Craig I've been ignoring it for many months but I've finally conceeded to the fact that it's not going to fix itself so decided to make a bit more of an effort.

Greg

Yea im in the same boat as you mate except the 2 mechanics ive been to have told me there unsure lol.
Mines alittle different but as its pretty jerky down around 2000rpm. It was weird at idle but has since corrected that and now i just have the jerkyness.

[shane_3800]

VE has 6x1=6

Each cylinder has a coil direct on top of the spark plug. Nice design but you can't get the coil off or change the spark plugs without taking the inlet manifold off first. I could test the coils if I had a factory spec to measure them to.

Fuel filter I would think would be noticeable under load not idle but I could be wrong.

O2 possibly. Are these in service on idle?

Craig I've been ignoring it for many months but I've finally conceeded to the fact that it's not going to fix itself so decided to make a bit more of an effort.

Greg

yes o2 sensors work at idle


maby idle solinoid is getting old

but i think it is a spark problem knock sensor might be faulty

[VECom]

I didn't think they had an idle solenoid but a stepper motor, not sure about it though The idle is rock solid on 600rpm, car just shakes. I think could be coil but not sure how to go about testing them.

The problem with many mechanics these days they didn't learn old school diagnosis, they just plug the diagnostic gear in and if it doesn't see the fault and tell them what to replace then they have no idea. I don't want to take it to a workshop for them to waste hours on it and charge me for loads of parts they've put on it trying to find the problem.

I'll do a bit more stuffing around and head scratching on the weekend

[Craig93]

I didn't think they had an idle solenoid but a stepper motor, not sure about it though The idle is rock solid on 600rpm, car just shakes. I think could be coil but not sure how to go about testing them.

The problem with many mechanics these days they didn't learn old school diagnosis, they just plug the diagnostic gear in and if it doesn't see the fault and tell them what to replace then they have no idea. I don't want to take it to a workshop for them to waste hours on it and charge me for loads of parts they've put on it trying to find the problem.

I'll do a bit more stuffing around and head scratching on the weekend

Yea for sure.
Let me no how you go man.

[shane_3800]

I didn't think they had an idle solenoid but a stepper motor, not sure about it though The idle is rock solid on 600rpm, car just shakes. I think could be coil but not sure how to go about testing them.

The problem with many mechanics these days they didn't learn old school diagnosis, they just plug the diagnostic gear in and if it doesn't see the fault and tell them what to replace then they have no idea. I don't want to take it to a workshop for them to waste hours on it and charge me for loads of parts they've put on it trying to find the problem.

I'll do a bit more stuffing around and head scratching on the weekend

im a young mechanic i hardley use the scantool i have been learing how to use gas benches and scopes but it is all to do with feel my boss can just say check this and bang that is usally the prob

most rough idles i have seen are spark plug or coil related

and yea i meant stepper motor

[LittleMissVE]

hmm my car idles at 550ish when its warmed up.

its my first v8, thought they all idled low?

Mine idles around 550 too... I read this yesterday & had to check this morning cos I've never even noticed.

[Michelson4301]

These things are FBW so no stepper motor. Coils are a possibility but it would be very obvious if a coil was dead or dying under full load as the increase cylinder pressures would take more coil voltage to jump the spark gap.

All V6 motors released in Holdens (I can't speak for other brands/countries) are inherently noisy and harsh. It is due to their design "flaw". I would suspect a sagged engine mount if they have been subjected to oil or you have highish kays ie. 80,000km+.

[VECom]

I did notice there was no throttle cable on it. How high tech the old commodore has got.

Under load it runs fine and it's as smooth as a bommodore is. Engine mount now that's a possibility. 104k so if that's a known problem then something worth checking. I'll jack the engine and see what happens.