Gerdas

Hi, please help, im having engine vibration problem on S6 5.2. While car is parked with engine on and shift is in "D" or "R" position, all is ok, but if shifting into "P" or "N" strange engine vibrations comes on and i can not find the problem..

Scanned for errors and found a knock-sensor fault and O2 sensor fault. Nothing more. Car also has a small oil leak, but its only a 2-3 drops per day, so im not sure i need to fix this one..

Replaced knock-sensor, engine oil, air filters, all spark plugs and so far no results- vibrations are still there. Ordered O2 sensor, but will have it in 1-2 weeks only and i dont think it causes vibrations. Also in a service they removed the intake manifold because also been changing one seal, and i seen that there is a small amount of carbon built, but it is so small that mechanics said it is not worth to clean it yet. Also car is doing 0-100 in 5.3 s every time, all cilinders are working, no errors of missfires.

Talking to different mechanics found out it can be a faulty engine mountings. Also i was adviced to try to dissconect the engine mountings wires and if engine vibrations goes away, it would mean the faulty mountings. One guy with S8 (same engine) said it should be a conectors somewhere under the hood in a front of the engine but i do not see any conectors there. Where are they located? And if they are faulty why there is no errors?
Also do you have any ideas what more to check?

Thanks.

FormulaElement

Carbon cleaning, engine mounts, transmission mount, vacuum leaks, AC system, torque converter. These are the sources of where your vibrations can come from. I would start with the mounts, carbon leaning and vacuum leaks before moving onto the last two as they're pricey.

Unless your a DIYer i would leave it alone as its very expensive to do anything on S6's.

Gerdas

There is no vacuum leaks- inspected exhaust manifolds carefully, all ok. Also the carbon amount is very low if to compare with photos people are sharing online..

And what about AC ? if everything is completely turned off- it does not effect vibrations at all... If so- can we say it is working properly? I heard audi AC is working all the time anyway, isn't it?

Will check engine mountings on my next visit to the service.

Is there any test or trick to check the torque converter?

FormulaElement

It hard to describe how the AC works, but yes technically its always on. But there is a actuator or something in there that controls how much pressure is being sent through the system.

In theory it's supposed to completely turn on off, but it can fail or wear down and cause the system to be more on/off than its supposed to be.

There is no way to test the torque converter and more than likely its not causing the vibrations, but it could.

Actually thinking about it, i would start with a new PCV valve and fixing the oil leak. The leak is probably causing pressure to escape form the engine and could cause vibrations as well.

Gerdas

Ok, and what about one failed pre-cat O2 sensor? Heard lots of opinions, but is it possible it can cause vibrations? as i know there are 4 pre-cat O2 sensors and other 3 is ok..

SchwarzS6

You can test the AC theory by turning it off. The AC can be turned off by momentarily pressing the ECON button on the climate control. You can turn it back on by pressing the Auto button.

AndreNY

wow upon opening this thread I was thinking here is another S6 guy with the same issue I had, but after reading your issue in detail its funny that my vibration was completely opposite of yours. My car when stationary and running was perfect in Park or Neutral but in Drive and Reverse I had a vibration similar to yours, in my case it was a bad Axle (inner joint was bad) I would assume in your case to be an Engine Mount
Good Luck

pr0xZen

Engine vibration only when drivetrain is relieved of tension, sort of points towards engine mounts or related brackets. Noticed any feel of weighty "play" when going on/off the throttle - like fairly noticable jolts when on/off the throttle in rush traffic?

Gerdas

pr0xZen, when D or R is engaged, whatever car is moving or standing in a place, there is no vibrations at all... I suspect the engine mountings too, as there has left only 3 things- mountings, one faulty O2 sensor and small oil leak. Leaving it in service on friday to fix the oil leak. Will see does that effects the situation anyhow..

I would just change the mountings without a questions but after i saw the prices im looking for a method to check them somehow before changing.

I talked to several technicians and heard the same opinion that hydraulic engine mountings can be disconnected and if the vibration gets smaller than it means faulty mountings. Does anyone tried to check them this way? Does such a testing really works?

Also today found out that when engine is warm and on idle rpm (600) it is something clicking/ticking near the throttle body on a passenger side. If to apply a little bit throttle at the 700 rpm it stops and no more clicking/ticking on higher rpm. I think it can not be a tensioner as they are located at the front of the engine. Removed the plastic pipes from the throttle bodies expecting to find some "play" of the closing caps, but it is working nice. Do not know can this sound be related to the vibrations. Even do not understand what part can be clicking there...

Anyway, on friday evening will see does the fixed oil leak effects the situation anyhow. If not- probably will have to purchase engine mountings

pr0xZen

Hopefully you'll take it to an experienced Audi mechanic that you trust not to push unneccessary parts or repairs on you. The majority of shops and mechanics won't do this, but both work and parts for these beasts are top dollar. Have them inspect the engine mounts while its in - shouldn't be too hard to diagnose for someone who knows their way around these engines, or electronic-hydraulic mounts in general (most modern diesels have'em too). If its a leak it should likely be rather visible, solenoids should make a slight sound if triggered, maybe not audible with engine running. Fixings could be loose or damaged. Also, could be damaged wiring. All in all I suggest you have the tech inspect the mounts, and if they find something wrong - have them show you the issue.

Does it vibrate only on idle, or if you change revs slightly, too? Sometimes a change in idle towards an unfortunate rpm range (usually a drop) can hit frequencies that will resonate vibration much worse than others. These active mounts should be capable of absorbing such, but only if working well and within reason - they're good, not magical.

As to the clicking sound - get a probe stethoscope. Cheap as nails, and very helpful when narrowing down the source of a single sound in a sea of noises (engine bay).