Lumpy VR6

[vw.classics 0]

I'm keen to get some opinions on various checks to be made to try and cure a very lumpy idle issue.

 

It's very lumpy from cold (and warm) right up to about 2500 - 3000 rpm - then seems to clear and revs clean and hard like a VR6 should. Having owned a couple of other VR's before I know how smooth they can idle so I know something is not quite right.

 

I've taken it to my local garage who have changed the sparks and said the leads look OK (as they were genuine VW red HT leads replaced approx 3 years ago) as the car has only done approx 3,000 miles over the last 3 years.

 

There are no overheating / oil or water loss issues so I don't think it's a head gasket although the garage are going to do a pressure test to rule that out too.

 

I've read some of the other related threads on here and I have also tried spraying a fine mist of water across the coil pack with no obvious signs of arcing so the coil pack seems to be OK and not cracked.

 

Any other pointers? There was a crankshaft sensor fault code showing which the garage has checked and said the sensor seems fine....

 

What else should I be asking the garage to look at??? MFA perhaps?

 

It has also been quite difficult to start when engine is up to speed / hot recently.

 

Any ideas or comments / previous similar experiences (and cures) would be really appreciated!

[floppyman 0]

Wow.... So many people having this problem now a days.

All your problems are already around the forum.

The crank sensor is normal to have as a fault code. When the engine is running the fault will go away. Thats how it works.

Your high idle is down to a air leak on the intake pipes ,blocked isv damper box or the isv itself.

Have a search for isv problems on the forum

[vw.classics 0]

Wow.... So many people having this problem now a days.

All your problems are already around the forum.

The crank sensor is normal to have as a fault code. When the engine is running the fault will go away. Thats how it works.

Your high idle is down to a air leak on the intake pipes ,blocked isv damper box or the isv itself.

Have a search for isv problems on the forum

 

Thanks - just to clarify there is no high idle issue. The idle is fine, just very lumpy!

 

It's just VERY lumpy up to about 2500 rpm then clears. It also doesn't like being under load e.g trying to pull from 30-40mph in 4th / 5th gear so almost like a misfire but not quite that bad.

 

Do you still think this is an ISV issue?

[vw.classics 0]

Any VR6 specialist garages near the Surrey/Sussex/Berkshire/London area that anyone could recommend?

 

Happy to travel further for any decent recommendations...

[dumptyboy 0]

Have you tried unplugging the MAF or lambda/oxygen sensor and seeing how it idles? Its possible that with the MAF disconnected the engine may cut out. The ecu will try to compensate for the sensor thats disconnected, and you might find that with the lambda disconnected it will idle fine.This would indicate that its possibly a sensor thats at fault. Have you changed the coolant temperature sensor by any chance aswell? Although im not sure if that would explain your problem.

I would say its either down to a faulty sensor, split hose or ignition/HT leads. But im no expert, and that doesnt really narrow your search either, haha. :)

[vw.classics 0]

Have you tried unplugging the MAF or lambda/oxygen sensor and seeing how it idles? Its possible that with the MAF disconnected the engine may cut out. The ecu will try to compensate for the sensor thats disconnected, and you might find that with the lambda disconnected it will idle fine.This would indicate that its possibly a sensor thats at fault. Have you changed the coolant temperature sensor by any chance aswell? Although im not sure if that would explain your problem.

I would say its either down to a faulty sensor, split hose or ignition/HT leads. But im no expert, and that doesnt really narrow your search either, haha. :)

 

Thanks - the garage tried disconnecting the MAF today and made no difference apparently.

 

Any other ideas out there??? From what I'm hearing this is a very common VR6 issue.

 

Advice please guys?

[Portent 0]

Any VR6 specialist garages near the Surrey/Sussex/Berkshire/London area that anyone could recommend?

 

Happy to travel further for any decent recommendations...

 

You could try S E Autoworks in Guildford. I've only used them once but I seen to recall that it's run by a couple of ex vw mechanics. It's fairly close to you.

 

I've got a spare maf if you wanted to try it... I'm near Esher.

[dumptyboy 0]

What about the ISV idle stabilisation valve? Have you tried removing that and cleaning it with carb cleaner?

[Kevin Bacon 5]

Thanks - the garage tried disconnecting the MAF today and made no difference apparently.

 

Any other ideas out there??? From what I'm hearing this is a very common VR6 issue.

 

Advice please guys?

 

Well that means the ECU has already bypassed it then, so suspect that as the culprit. And before you say "it was replaced x months / years ago", it doesn't make a jot of difference. When they go, they go, and are impossible to diagnose properly.

 

As Floppyman said, this has been covered countless times already. Poor running, lumpiness, stalling can all be attributed to the MAF.

[vw.classics 0]

Well that means the ECU has already bypassed it then, so suspect that as the culprit. And before you say "it was replaced x months / years ago", it doesn't make a jot of difference. When they go, they go, and are impossible to diagnose properly.

 

As Floppyman said, this has been covered countless times already. Poor running, lumpiness, stalling can all be attributed to the MAF.

 

Thanks - so just to clarify, are you saying the MAF is the culprit OR the ECU?

 

Any way of testing before I buy a replacement?

 

Cheers

[floppyman 0]

Well that means the ECU has already bypassed it then, so suspect that as the culprit. And before you say "it was replaced x months / years ago", it doesn't make a jot of difference. When they go, they go, and are impossible to diagnose properly.

 

As Floppyman said, this has been covered countless times already. Poor running, lumpiness, stalling can all be attributed to the MAF.

 

+1

If disconnecting the maf doesnt make a difference then i would start with that.

 

And if your near Portent then its a good offer to try another one without spending ££££

[Kevin Bacon 5]

Thanks - so just to clarify, are you saying the MAF is the culprit OR the ECU?

 

Any way of testing before I buy a replacement?

 

Cheers

 

Yep, the MAF. If unplugging it with the engine running makes no difference, the ECU is already using the throttle potentiometer as it's main load measurement, which isn't very accurate and will cause some running issues.

 

MAFs are virtually impossible to diagnose unfortunately. They either work or they don't. Trying a MAF from a known good running VR6 is a cheap way to test it, but not always possible.

[vw.classics 0]

Yep, the MAF. If unplugging it with the engine running makes no difference, the ECU is already using the throttle potentiometer as it's main load measurement, which isn't very accurate and will cause some running issues.

 

MAFs are virtually impossible to diagnose unfortunately. They either work or they don't. Trying a MAF from a known good running VR6 is a cheap way to test it, but not always possible.

 

Thanks guys - just double checked the MAF with the garage and apparently there was a significant change and the revs did drop when the unplugged the MAF.

 

Any ideas on what next to check as it seems the MAF is not the issue?

 

Cheers

[vw.classics 0]

You could try S E Autoworks in Guildford. I've only used them once but I seen to recall that it's run by a couple of ex vw mechanics. It's fairly close to you.

 

I've got a spare maf if you wanted to try it... I'm near Esher.

 

Thanks for the offer mate - I mate take you up on the offer. Is it easy to swap over and fit?

 

Don't suppose you have a spare coil pack that I could try and swap over / test also? I've heard that despite the usual tests it may still be worth trying a different coil pack too.

 

Cheers

[4eyes2wheels 0]

Is it easy to swap over and fit?

 

Yes it is an easy swap - I am a total klutz and swapped mine without a problem.

[vw.classics 0]

Yes it is an easy swap - I am a total klutz and swapped mine without a problem.

 

Thanks for that - any pointers on "how to" remove the MAF and coil pack would be appreciated...

 

Cheers

[daleyboy 0]

Mate its not difficult, just have a go.

[AlexDG 0]

Have you changed the fuel filter (next to the rear O/S wheel) recently?

 

It may sound mad, but I had identical symptoms, and at the time changing the fuel filter was on my to-do list, so figured since the fault was either fuel or ignition related I may as well change the filter to rule it out...it resolved the problem (this was the only thing I changed).

Edited November 1, 2012 by AlexDG

[vw.classics 0]

Have you changed the fuel filter (next to the rear O/S wheel) recently?

 

It may sound mad, but I had identical symptoms, and at the time changing the fuel filter was on my to-do list, so figured since the fault was either fuel or ignition related I may as well change the filter to rule it out...it resolved the problem (this was the only thing I changed).

 

I haven't tried changing the fuel filter yet....so will give it a go to rule it out. Thanks for the heads up.

 

I had a replacement coil pack fitted last week and it does seem a lot better...but still runs VERY lumpy on start up from cold, albeit less juddery under load and lower revs now so I think it has helped. It is very difficult sometimes to start after a long run / when the engine is warm.

 

Does the issue with difficult hot starting sound like it could also be related to fuel filter or electrical?

[krishen 2]

I haven't tried changing the fuel filter yet....so will give it a go to rule it out. Thanks for the heads up.

 

I had a replacement coil pack fitted last week and it does seem a lot better...but still runs VERY lumpy on start up from cold, albeit less juddery under load and lower revs now so I think it has helped. It is very difficult sometimes to start after a long run / when the engine is warm.

 

Does the issue with difficult hot starting sound like it could also be related to fuel filter or electrical?

 

As mentioned before, id clean the ISV and see if that cures the problem. Cheap and easy fix (if it is the issue)

[AlexDG 0]

Starting was worse when cold on mine, though rough running and stalling happened both hot and cold.

 

I haven't taken the time to understand the logic behind the symptoms and why a fuel filter change fixed it. It could be that the similarity of symptoms is a coincidence, but since it is a service item and relatively cheap job to do it has to be worth doing to rule it out?

 

I cleaned the ISV prior to changing the fuel filter and it made no difference (it had been cleaned a few months prior to the fault as well).

[vw.classics 0]

Any pointers on where the ISV is located and how to remove / clean would be appreciated :)

 

As mentioned before, id clean the ISV and see if that cures the problem. Cheap and easy fix (if it is the issue)

[krishen 2]

Any pointers on where the ISV is located and how to remove / clean would be appreciated :)

 

Here you go.

 

http://the-corrado.net/showthread.php?32869-VR6-Idle-Control-Valve&highlight=isv