VS Ecotec rough idle

[primo]

Hi Guys,

This one is a real challange that not even two different qualified mechanics can work out on my 98 seriess II V6 Ute.
I have had a rough idle over the last month that we can't diagnose. It drives beautifully and really smooth, but when coming to a stop it starts to misbehave. Driving off is fine. I have checked all the previous posts (they were really useful) and taken it to various mechanics with no luck and no error codes showing up!. This is what I have done to it over the last couple of months usually with genuine parts-

Replaced Fuel pump & filter, CAS, IAC, temp sensor(tte little one not the larger sender?), Fuel pressure regulator, Oxygen sensors, manifold gaskets.

Removed & cleaned Throttle body, plenum chamber, manifold, injectors where sent away for a proper clean, spark plugs checked, starter motor. Checked the vacum and purge hoses especially the ones connecting to the TB.

The above has certainly improved it's performance and starting but that rough idle is still there!

Would like some further advice on a likely cause. I'm thinking whether a compression test is valid?

One other thing, with the two purge/vacuum hoses that connect to the module towards the back of the intake manifold, how do you know in which order the hoses connect up? ie, there are two connectors, one goes off to the Throttle Body and the other one to the carbon canister, I have the bottom one going to the TB and the top one going to the canister?

[FstStig]

Have you tried cleaning or replacing your TPS (Throttle Position Sensor)? Cleaning or replacing your MAF (Mass Air Flow sensor)?

[primo]

no I haven't. The mechanic said he tested the TPS resistance and it was ok. How do you clean the two TPS and MAF? carby cleaner or just wipe any dust with a rag when taking them off as I hear they are delicate things?

[nathanVY]

I wouldn't think the TPS would contribute to idling issues. MAF possibly though, you can buy maf cleaner, whether it's worth it (or safe) is another question. Wiping it down with a rag can't hurt though.

Join the club with the crappy idle too, mine does it to really bad. Seems to get worse once it's warmed up.

[FstStig]

Are your engine mounts not stuffed? Just throwing this idea out there but possibly your CAM angle sensor?

[primo]

replaced the CAS about two months ago. The mechanic "checked" the engine mounts and reckons they look ok.

[FstStig]

By CAS do you mean Crank Angle Sensor or Cam Angle sensor, both completely different sensors in different locations.

[primo]

sorry I meant the crank angle sensor was replaced a while ago

[FstStig]

ok get him to check the CAM angle sensor.

[primo]

curious what the CAM angle sensor has to do with idle? I will check it out though.

[nathanVY]

engine mounts can "look" ok, but you'd have to really compare it to a new mount to see. if they've never been replaced guaranteed the engine will be sitting lower. good way to check is to get a mate to put the car in drive and full brake and give it a bit of a rev (be careful obviously) with the bonnet open. see how much the engine lifts, if it lifts heaps then your mount is either snapped or sagged or old or all of the above lol.

think about it, when the car is going forwards (drive) the passenger side mount is under strain... that's 90% of the cars life.

[primo]

yeah good point...............................I read about the mounts in another forum, so I'll check that out as well. The mechanic said that the mount bolts where tight so he didn't think they needed replacement, but if they have sagged, especially on one side, that could contribute to some vibration at idle I guess.

[nathanVY]

yeah I reckon that's the go with mine, the engine lifts a fair bit. so I'm gonna replace mine and hopefully the vibrations end

Harmonica balancer could be the culprit as well. Could be showing its age and throwing things out a bit at low rpm.
How many kms on your car?

[primo]

around 180,000.

[nathanVY]

mmm harmonic balancer could be contributing, they usually go around 200,000

[primo]

wouldn't the balancer being making noticeable noises or movement in general?

[nathanVY]

wouldn't the balancer being making noticeable noises or movement in general?

only if it's about to fall off lol. balancer will give you shudders and vibrations, usually decreasing with the increase of rpm.
if you start your car and take a look at how much the balancer wobbles about, i don't think they're meant to wobble at all.

[FstStig]

If this was the case wouldn't the ECU be throwing a code because the CAS would be getting an incorrect signal?

[The1]

nar the metal shroud the passes by the cas would be still fine, the rubber to the pully would be outta whack.

[gendi]

my VS idled rough and vibrated really bad, got the engine mounts replaced (both where split in half) and wow i didnt know my car could be so quiet and not shake, also car ran like a bitch due to my break booster vacuum leak.

[EDGE3]

Yes the car will vibrate badly if the engine mounts are gone,but it wont idle roughly because of engine mounts,idling and vibrating are 2 different things altogether,it would have definately been contributed by the vacuum leak

[nathanVY]

gendi how'd you test if you brake booster was faulty? I'd say my car is actually idling ok but just vibrating... so really keen to get the engine mounts replaced

[gendi]

i could hear a vacuum leak everytime i applied the brake. had a mechanic look at it and thats what he said it was, so i replaced it and been fine since, grabbed a second hand one from the wreckers took about 10 minutes to install.

found this in a different thread: posted by Brett_jjj

first try disconnecting the brake booster vacuum line from the booster,then block it off with your thumb and run the engine,keep it blocked and see how it runs then,if it runs fine,the brake booster diaphram is probably faulty.

[RX25SE]

@OP

Mine used to do this at around the 180k mark. It was almost stalling shifting from drive to reverse as the idle was so unstable.

Remove the DFI and clean/replace the zinc oxide grease underneath it.
Remove the DFI mounting bracket and clean the mounting surface for the module and the mounting points to the block.
Clean the block where the bracket bolts on.

The problem is the DFI develops an earth fault due to a small amount of corrosion between these points. Also the grease goes hard so it is less effective as a heatsink.

Once this is done, disconnect the battery for about 20mins to clear the memory.

[primo]

Hi Guys.............another long one but pls bear with me :-)

Just thought I'd give an update. The very rough idle is still bloody there. It does drive smooth as though.
Listed below what I have done thus far
and welcome any further suggestions. In a kind of weird way i enjoy the challenge of working out what the
problem is, even if it's driving me up the wall. I have bought the Gregorys manual.

Error Codes -

I received codes for the first time the other day, 22 & 23, relating to TPS and Air temp sensor. Cleared them and haven't received the errors since. I am replacing the ATS tonight.........the TPS is $170 from Holden!

Replaced so far with new genuine parts -

Fuel pump, fuel filter, CrankAS, CamAS, IAC, temp sensor and temp ECU sender, Fuel pressure regulator,
o2 sensors, new leads, checked plugs,injectors professionally cleaned,

Checked and or Cleaned -

removed manifold and plenum, cleaned inside out with new gaskets.
removed and cleaned Coil packs and checked resistance, engine mounts(mechanic told me they are ok but do I trust him?),
Harmonic balance feels and looks strong, ie, no play or wobble.
Chcked manifold purge hoses, swapped them around at the purge solenoid in case they need to be in some
order? One goes to the TB the other to the canister.
Removed and cleaned the starter motor and contacts, was black as but now starts beautifully!

Still to Check -

Cylinder Compression ?
Remove and clean the DFI (have removed and cleaned the coil packs and resistance ok) ?
ECU ?
May take the tank(ute) back out as one of the vapour hoses running from top of tank to the bottom near the return hose wasn't connected.......assuming this needs to connect to the canister vapour hose coming from the
canister in the engine bay?
anything else I am missing ?