SimonG

Hi again guys

I've been a member here for almost 9-month now, and the help and support offered by this forum is superb.
My A6 is a superb car and definately the best vehicle I've ever had the pleasure to won, however, there's a few things that have been niggling me over tha past months that I never resolved ....

- Engine RPM's -
Does anyone know why my engine RPM's drop when erver I activate anything electrical?. I can see and feel the RPM's drop when I open/close a window, use the hazard lights, turn on the stereo etc.
This is even more pronounced when turning on the air-con - Now I'd expect this to a certain degree, but sometimes this can cause the RPM's to flutter so much that the car can kangeroo when trying to pull off slowly.
I replaced the battery recently but this made zero difference.
I've done 10k miles in the car with this issue and it's not gotten any worse or better.
Any ideas?

- Fluttering sound -
Over the past few months I've noticed a faint fluttering sound when the engine is under load. I can't tell whether this is from the transmission (CVT Auto) or Engine but I think it's got a little worse recently.
I recently had a CV boot replaced but the mechanic said the joint was still good.
Anything else that could cause this?

- Vibration -
A few months back, I noticed an odd hum/vibration when the RPM's hit between 1500 and 2500. It doesn't appear to be present outside of this rev range. The vibration/hum has worsened recently, the prob is it's difficult to pinpoint where it's coming from as sometimes I think it's from the rear and sounds exhausty, whereas other times it seems to be from the engine.
Has anyone had similar issues?

At this time the above issues are minor annoyances, and my wife doesn't even notice anything when she drives. However, I want to make sure there's nothing nasty brewing.

Ohh...the cars a year 2000 A6, 2.4ltr V6, CVT M/tronic with 104k miles on the clock - It's 2k miles overdue for a service and I'll be getting this done in the next couple of weeks.

Many thanks

SimonG

Any advice greatly appreciated !

Edd W

<center><img src="http://seiryuu.org/~etoile/art/girly.jpg"></center><p>you will get loads of poeple reading your post and you may get a few answers.

I would say that the iddle issue is possibly due to the cam timing being out. The 2.8 is very sensitive and the 2.4 will be even more so. It has loads of inlet valves for a small capacity engine. The air flow per valve, at idle is so low it can make it very suseptable to stalling and if the cam timing is out it will be even worse. The problem is that any additional load causes the idle to drop and before the ISV (idle stabilisation valve) can cut in, the engine dies.

The idle control uses ignition timing as well to speed up the engine when it has extra load on it.

The only other thing I can think of is the control of the CVT transmission. If you put it in neutral, does it still do the same things?
At idle the drive to the transmission from the engine should be disengaged but if it is not fully disengaging it would cause all sort of idle issues. Does the car creep forward at all without any thrttle applied?

The noise could easily be the cam belt or the ribbed belt beginning to break up. It could also be one of the tensioners or even from the gear box. It is a case of trying to establish if it engine speed or road speed related. We need more info.

the vibration could simply be the natural harminic vibration all V6's have. It is simply a consequence of the machanical compromise that is a V6 engine. No mechanical engineer really wanted to build a V engine of any kind. All of them are a compromise based around the desire to fit more cylinders into a shorter space. More cylinders demanded by marketing departments and shorter space demanded by body designers. The perfect engine is a relatively small capacity straight six. This is the almost perfect design and can be so smooth vibration is almost non-existant at any revs. The 90? v6 in Audi's tends to have a vibration at about 1700rpm which is noticeable when gently reving the engine while stationary. It is not bad enough to warrant a balancer shaft but it is quite easy to feel. If everything on your car is otherwise working normally and the vibration is around 1700 rpm (it may be higher or lower on the 2.4) then that is all it is I would guess (this is my caveat).

SimonG

Thanks for the tip

With regards to the idle problem - If the cam timing is out slightly is this something simple to fix?
The prob's been with the car for the last 10k miles (probably a lot more) and is more of an annoyance than an issue.
Incidentally, why would cam-timing cause an RPM drop when something electrical's turned on (Windows etc)?.

The rpm's drop regardless of whether in/out of gear, and yes, the car does creep when in gear with no throttle but I believe this is notmal with the Audi CVT box - They programmed creep into it to make it feel more like a traditional auto box.

Ref the fluttering noise - Now you've got me worried !!
The cam-belt was replaced at 78k miles (now at 104k). The noise is very faint and my wife can't hear it, but it'd definately there. The best way I can explain it is like a very faint but rapid .."fft..fft..fft..fft.." sort of noise. It's only apparent when accelerating so difficult to say if it's gearbox or engine related.

With regards to the vibration - The car didnt do this when I bought it. The hum/vibration happened one day a few month back when pulling off onto a roundabout and has done it ever since.
You can feel a vibration at the same resonance as the hum through the accelerator pedal - again, my wife can't detect it but I know it's there.

An ex-Audi mechanic who drove the car a few weeks back (Fixed the CV boot) didn't detect any of these issues and said the car was one of the nicest he'd driven ...... maybe I'm just being over critical of a 5yr old/ 104k mile car?

Edd W

a leaking exhaust manifold gasket or could simply be a loose spark plug.

I would check all the plugs - remove them one by one then clean up the thread, apply a little copper-ease grease to the thread and re-torque them to the correct torque. This could explain the slight vibration as well as the sensitivuty to idle variation.

The reason cam timing could cause the revs to drop is because when you turn on any electrical item, it creates an extra load on the alternator. This normally is compensated for by the idle control system which can increase the amount air allowed into the engine - like opening the throttle slightly, and it can also advance ignition timing which again, will increase the engine speed. If however, the cam timing is out, the engine could be producing so little torque at idle it dies before it manages to respond to the normal methods of increasing the speed.

I know that my wife's A6 2.8q whihc we have just sold could stall at idle, simply by truning the steering to full lock. I suspected the cam timing was slightly out but otherwise it ran really well and possibly benefitted from a bit of extra torque at higher revs. I did not fit the new cam belt on that, it was done by Derby Audi before I bought the car and I never got around to checking it with the cam locking bar.

SimonG

.. I'll get it checked when it goes in for it's service