Help please. Slightly erratic idle and knock on tickover

[g60leigh]

Can anyone throw any suggestions please?
Car is ticking over and 900rpm but seems to hunt every now and again.
Also there seems to be an intermittent knock from bottom of engine near the gearbox. This only happens on idle.
No fault codes on vag com and car is driving fine.
Oil and water etc are all fine as well.
I have no idea what this could be.

Thanks.

 

[g60leigh]

Also it does not seem to happen when I have the climate control on???

 

[ruffrida]

Does the noise go away if you put the clutch in?

Possible clutch release bearing??

 

[Westy]

If in neutral it sounds like clutch or release bearing. Turning the aircon on puts more strain on the engine so you will notice the rattle more. Do you know what flywheel you have?

Rev hunting can be a number of things. Boost leak, clutch pedal switch, throttle body needing alignment.

 

[s3dave]

Revs hunting from idle will be a vacuum leak of some sort, is your inlet manni tight? if so the usual leaks are under the manni

The knock you hear will be the DMF i would imagine, when the engine alters revs ....

 

[g60leigh]

It goes when air con etc on. Just feels like tick over a bit low. Gonna see if it goes with clutch in tomorrow. Sorry but what is the dmf?

Thanks guys.

 

[g60leigh]

Guessing is dmf dual mass flywheel?

 

[tyson]

I have the same trouble with mine. My car is idling at around 700rpm which causes panels to rattle! Turning the aircon sorts it so i have been driving with aircon on for the last 2 months.
the problem started once i changed my sparkplugs

 

[Greg-S3]

When pulling off in first can you feel the car wobble? A dual mass that has gone in a big way can give poor idle quality, I've seen it numerous times on cars, it basically un balances the engine

 

[tyson]

Yeah. I hve an almost judder coming from what seems to be the clutch area. My clutch has definately gone as it slips drastically when flooring it. Didnt think that could affect the idle though

 

[Greg-S3]

Yes mate dual mass can effect your idle as the flywheel is working against the engine, as it's bolted to the crank the flywheel adds extra inertia so it make the crank spin fast, slow, fast, slow etc and slightly changes the timing hence a lumpy idle. And the dual mass is your wobble when first pulling away

 

[g60leigh]

I have not notice any wobble at all.
Been away all day today but gonna try a bit of experimentation on way to work tomorrow.
If it has gone. Is it best to replace with a direct replacement or is there an upgrade option worth considering? Thanks.

 

[ruffrida]

Could this be the same problem i am having.

On idle car seems to shack like mad with revs going up and down by a few 100revs, also rattles like hell.

Also this morning when i was driving it would sort of jerk itself along like it was really sloppy??

 

[badger5]

dual mass flywheel dying maybe?
gbox end noise?

 

[ruffrida]

dual mass flywheel dying maybe?
gbox end noise?

Yeh gearbox end, makes the ****** car shake

 

[ruffrida]

Well new flywheel and clutch fitted but revs are still very jumpy on tick over, and car surges on/off on low revs, the rattle has now moved to the drivers side / cam belt side, it also died twice on me yesterday no notice just died and it also stopped reving, came round a round about and the was no power through the peddle until i dipped the clutch and all came back to life!!

 

[A3dan2907]

I had a similar problem with an a3 I had where it would die on me as I was driving it turned out to be a vacuum leak and maf sensor was gone