A6 auto revving slightly

[tubbsy99]

Hi all,

I have noticed something strange with the A6 this past week. When I amdriving at a steady speed and take my foot off the accelerator, like normal therevs drop to around 1000 rpm. But i have noticed at this point something thatfeels strange to me, the car revs gently between 1000 rpm and sometimes up to1200/1250 rpm and continues to do this until i either slow down or i put myfoot on the accelerator again. It is almost as if the car is hunting for anidle if that makes sense. Normally this wouldn’t bother me but where the car isgently revving you can feel a rocking motion as such due to the revving. It’senough to be annoying and wanted to find out if anyone else has this problem oreven if it is a problem.

The car has just had a full service by my garage and the following changed:

Full service

Oil and filter change

Air fliter change

Gear box oil and filter change

Fuel filter change

Coolant change

diff oil change

Power steering oil changed

Brake pads changed and brake fluid changed

I did take it back to the garage and they found a fuel pressure regulatorfault code or something to that effect. They siad this might have been due tothe new fuel filter being changed. They cleared the code but the problem stillpersists.

Any ideas guys?

Cheers

Tubbs

[saltyseaman]

I have noticed that mine does it too.
Although at higher speeds when you lift off the throttle, the car seems to coast more with little or no engine braking.
Its only at lower speeds when I lift off the throttle that the "problem" you describe exists. I have almost convinced myself that its just the auto box deciding whether to downchange or not?

I have a 3.0 TDI auto Le Mans

[Peter D]

Turn the A/C off for a few days and see if it still revs by itself. Regards Peter

[gianton]

This happens to me only when I go downhill and the engine is cold. Once the engine is warm this doesn't happen.

[saltyseaman]

Yep! forget what I said, I have to agree with what Gianton says. I just went out to the park with the dog and on the way back when the engine was up to temp, it didnt happen.
What causes this? I have no idea.

[gianton]

Might be a way to warm the engine faster. Diesels engines get warm harder than petrol ones.
Maybe someone with a petrol engine can chime in to confirm that.

[Guest 2]

Can't say I've noticed this myself when driving. My engine is currently warm so I will have a look when its cold.

[gianton]

I live on the top of a hill and every morning I have to drive downhill on the way to work. This revving up and down was from the day I got my car 4 years ago. I remember my ex BMW 528i wasn't doing that.

[Guest 2]

Noticed this morning that my car does this too, never noticed it before until the question was asked.

Seems to be normal :)

[tubbsy99]

The slight revving wouldnt bother me at all, its just the hesititation in the engine that makes the car feel like it rocking back and forth slightly when not accelertaing that is a little annoying. It just doesnt feel smooth, this being my first auto i have nothing to compare it with but ive never experienced this feeling with any other car even when as a passenger in an auto.

I did take it back to my garage and they did find a fault code which was the 'fuel pressure regulator' (didnt get the code unfrotunately). They said this might have logged when they changed the fuel filter. They cleared the code but it still does it. They have the car again to do a deaper check. I will let you know if anythign comes up guys.

Tubbs

[tubbsy99]

Could it be something to do with the fuel pump? Personally i didnt think it was as the issue is only noticeable as i have mentioned. Idle is spot on and normal driving when accelerating is fine as well. If it was the fuel pump i would assume it would do it all the time.

Tubbs

[Getaway_Driver]

Mine does it too - I agree with Chris and think it's normal. :-) (means I don't have to think about any potential issue) also I ran a full VCDS check and all is well.

Good luck getting to the bottom of it.

[tubbsy99]

Well my mechanic took the car to an auto electrician today to do a full scan on the car which should have shown any fault codes. The car did not have any codes coming up and they took it for a 20 mile drive around the local area and could not find anythign wrong with it. They said the car drives brilliantly and whatever i am sensing in the car is nothing to worry about. Guess it must just be me then :-)

[tubbsy99]

Well a couple of days ago the garage had the car and run afull check and couldn’t find anything wrong and it’s still doing it. Havingnever owed a Audi or an auto before i just put it down to how the car behavesbut, my car is with Audi today for a radiator sensor switch recall which theyare doing under warranty and i have one of their 11 plate Audi A6's for theday. This is also an auto and when driving it does not have the revvingissue and is very smooth to drive which leads me to believe there is somethingwrong with mine.

I’ve asked the Audi guys to have a look at it as a favour asi don’t want them charging me a fortune just to have a look at it. They mightspot something immediately but it’s really bugging me. The hesitation in theengine when it does it just makes the ride a little uncomfortable and i find iam having to change my driving style to stop it happening. Surely and errorcode would be present?

Tubbs

[Guest 2]

Is the 11 plate the new C7? Also on either the C6 or C7, dependant on the engine and drivetrain it may have a Multitronic or S-Tronic gearbox where ours is Tiptronic.

Let us know if they find anything.

[tubbsy99]

Hi Chris,

Not knowing much about the differences im not sure but the interior and exterior look are the same as my car and the MMI is pretty much the same (although the screen looks a little clearer). The hire car also has the same paddle shifters on the steering wheel like mine.

[Guest 2]

Sounds like its a C6 then, do you know what engine is in it?

[tubbsy99]

I cannot see any markings to say which engine it is but it is the TDI and judging by the power it is probably the 2 litre.

[Guest 2]

If its 2 litre then it will have the multitronic box which is a CVT.

I dont like the feeling of the CVT as you have probably of noticed, it keeps the revs steady but you gain speed (weird feeling) so it wont shift like the Tiptronic and is probably why you cant see the revving.

[tubbsy99]

I know the cars are completely different so veryhard to make a direct comparison but the experience in the hire car has shownme what it generally should feel like and the revving in my 2.7 is certainlynot as comfortable. My car just feels like it has hesitation when no gas isbeing applied and the car should go back to idle. When no gas is being applied shouldn’tthe car just go back to idle (800 rpm) or thereabouts? It does when I come to acomplete stop but when in motion it sits at around 1000 rpm and revs upto1200/1300 rpm

[tubbsy99]

Ok so the dealer has come back to me and said they technician has test drove the car and can feel the problem i have and it is not normal. He has checked for error codes and found nothing and they have no idea what the problem is. They would now need to complete diagnostic checks on the car to even begin to find out what is wrong, oh and at £120 + VAT per hour. I’ve told them to not bother as i can’t justify someone scratching their head for an hour while the bonnet is open. Anyone know an experienced Audi specialist that might be able to help for less? Im in the Croydon area.

Just thinking............ could it be a dodgy fuel filter? They fitted a new one on the service but could this cause the issue maybe?

Only had the car three weeks and beginning to regret it!

Thanks

Tubbs

[Peter D]

I would be suspecting the MAF ( Mass Airflow Meter ) these can cause this problem and do not show an error code as it has not actually failed. An independant may well change it for a spare to try it out, Audi just want to empty your wallet. Regards Peter

[tubbsy99]

I didnt even think about the MAF. Do you know how much these might be to replace? I assume it only has one but being a V6 im not sure.

Stupid question - is a MAP and MAF sensor two different things?

Thanks
John

[Peter D]

I suggest you post up your engine code form the ID label in the spare wheel bay like AFN or AVF. It is on the lhs of the laber near the upper section and followed by ----XYZ which is the gearbox code. Regards Peter

[tubbsy99]

The codes on the label were as follows:

Engine: BPP
Transmission code (i think): HNN HST

There was another code as well 4F2 092

Are these the ones?

[Peter D]

Air mass meter -G70 Drivers side mounted in the side of the air pipe coming out of the air filter box, but it could be a manifold flap motor twitching and several other things. Regards Peter

[tubbsy99]

Sounds like its going to be hard to pinpoint without changing a number of componets and seeing what works.

[tubbsy99]

Hi All,

I am going to take the car to the garage tomorrow to check the servicing parts they changed in case any are no functioning. So i can give them some help advice on other possibilities can anyone help with what else it could be like Peter mentioned the air mass meter or manifold flap motor. Just helps save on time i guess.

Tubbs

[tubbsy99]

Hi all,

Been on holiday for a couple of weeks so haven’t been able to solve the carissue until now. We still couldn’t solve the problem and so i bit the bulletand took it to Audi to see what they say doing some diagnostic checks.

According to the technician it’s a problem with the gear box oil that waschanged by my local garage during the last service. My car has the triptronicgear box which apparently never needs an oil change but they have used themultitronic gear box oil instead which is completely different!

I will need to speak to my local garage as they will need to pay to sortthis out but i have a few questions:

1. Is it right that the triptronic gear box oil is never changed?

2. What lasting damage may have been caused by wrong oil being used? I am worriedthat a couple of years down the line the gear box might go bang on me becauseof this.

This error is not my fault so i should be held responsible for the costs buton the other hand I don’t want to change the gear box if it doesn’t have towhich is a considerable expense.

Just to replace the oil is pricey. They need to flush and replace the oil 2times which is 16 litres of oil @ £28 a litre! Then the 4 hours labour.

[saltyseaman]

Hi Tubbsy
Glad to here there is a cause to the revving, kind of. As my car does this too I must say I'm a little concerned if any damage can be caused.
I took out a third party warrenty for engine and gearbox but it stipulates that the oils used are per manufacturers reccomendations.

Anyway, if you go ahead and flush/change the gearbox oil and it cures the issue, let us know as I would probably end up biting the bullet and doing it too.

Only had the car a few months and the dealer serviced it before we picked it up. Previously it was all done by audi.

cheers

[aquatoo]

My 2.7 Avant does this sort of hunting on the overrun but only when the cruise control is on. If, for instance, the cruise setting is at 30, I haven't braked and am doing a higher speed it will sort of try to cruise at a higher speed. If I touch the brake or switch out the cruise it will then immediately decelerate normally.