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Discussion Starter #1
Hi couldn't find anything regarding this so hoping you guys can help. On my 2009 3.0 tdi s tronic whilst driving every so often the revs fluctuate by around 500rpm, idle is fine and smooth and no fault codes. I first noticed this whilst using cruise control, the speed was staying the same but the revs were fluctuating by 500rpm since then I have been monitoring more and this happened again whilst normal driving (not cruise control) This doesn't occur every time I drive, could it be the car is doing a DPF regen?

Thanks in advance
 

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hello robin,

unless you car is changing speed or gear it is not possible for the car to move the revs. the engine revs and gear is directly related to the speed you are travelling at unless you got a torque converter playing up. it could be an issue with the sensor if i had to take a guess.

also what gearbox have you got?
 

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I have exactly the same issue with mine. Its been doing it since new, and ive taken it into the garage for this and they couldnt find anything wrong. There are no Software updates available for it, and it doesnt do it all the time. Like you say, its noticable when driving with cruise control on, set speed, in 7th, and the revs fluctuate. I thought it was the clutch slipping, but on a brand new car? Still not solved, so i'd be interested if you do find out whats causing this.
TP
 

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Discussion Starter #4
hello robin,

unless you car is changing speed or gear it is not possible for the car to move the revs. the engine revs and gear is directly related to the speed you are travelling at unless you got a torque converter playing up. it could be an issue with the sensor if i had to take a guess.

also what gearbox have you got?
Gearbox is S tronic if sensor related would have thought it would have shown on the fault scan
 

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Discussion Starter #5
I have exactly the same issue with mine. Its been doing it since new, and ive taken it into the garage for this and they couldnt find anything wrong. There are no Software updates available for it, and it doesnt do it all the time. Like you say, its noticable when driving with cruise control on, set speed, in 7th, and the revs fluctuate. I thought it was the clutch slipping, but on a brand new car? Still not solved, so i'd be interested if you do find out whats causing this.
TP
I was thinking could be carbon related but if it's from new on yours doubt it's that. I already booked my carbon clean before this so will report back after that.
 

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If you've cruise control on, the revs will fluctuate. As the car/engine are under different loads, uphill/downhill/level etc. The engine has to compensate to keep your speed at the your preset level, for example going uphill the revs will need to rise & going downhill the revs will need decrease?
 

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If you've cruise control on, the revs will fluctuate. As the car/engine are under different loads, uphill/downhill/level etc. The engine has to compensate to keep your speed at the your preset level, for example going uphill the revs will need to rise & going downhill the revs will need decrease?
David, I'm afraid you are wrong. If travelling at a fixed speed the revs do not change unless you change gear or in fact accelerate or decelerate. What does change is the amount of fuel the car burns as you go up/ down hill. As each gear is fixed a revolution of the engine corresponds to a fixed ratio of wheel speed in the same gear.
 
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At what speed do you experience this? Is it just one particular range? I have a '01 Golf that would do this if I set the cruise control at a very low speed (around 40 mph I think). I think it's because at this speed the car is right at the edge between the 3rd and 4th gear, and since the cruise control is just focused at maintaining a particular speed, it might downshift or upshift depending on the road condition (going up hill, down hills, wind, etc.)

It could also be your clutch. The transmission might have low fluid level (due to leak, improper fill), old/burnt fluid, internal electronics that's starting to go (worn out solenoids, loose connection), or a small tiny imperfection within the valve body which causes the fluid pressure to fluctuate.

Have you ever changed the fluid and filter on the transmission? If you haven't, it's probably a good time to do it anyway.

Although not directly related, my A3 w/ the S-tronic transmission was downshifting a bit rough between 3rd and 2rd, but a fluid and filter change improved it dramatically.

Alex
 

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Robin, this may be a stupid question, but are you actually hearing the change in revs, or only seeing it on the rev counter? I ask because I had a similar problem years ago on my old Jag. Turned out that the sensor that picked up revolutions (on the flywheel, from memory) and fed data to the rev counter was playing up. Replaced the sensor and the problem went away.
 

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Discussion Starter #10
This has occurred on moterway and local driving so not affected by speed or the use of cruise control. According to the service manual the s tronic oil was changed about 6000 miles ago by an indie I have owned the car for the last 4000 miles. As refined as the A5 is I cannot hear the engine much whilst driving I noticed the fluctuations on the Rev counter rather than heard it. Car still drove smooth as normal. My warranty expires in a month so was hoping to get it sorted but doubt the garage will be able to find the problem as it's hard to replicate the problem
 

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Mine also does this and yes it is audible, that's how I normally know it happens although sometimes you can feel the car doing it.

I always associated it to a certain speed and the car not being warmed up.
 

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Discussion Starter #12
Mine also does this and yes it is audible, that's how I normally know it happens although sometimes you can feel the car doing it.

I always associated it to a certain speed and the car not being warmed up.
I was looking for it more this morning and did notice the sound (had to open the window) but was only for a few seconds then went away. I guess its something I will have to learn to live with.
 

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I was looking for it more this morning and did notice the sound (had to open the window) but was only for a few seconds then went away. I guess its something I will have to learn to live with.
Have you checked to see if the car changes gear when it happens? It should show the gear you are in on the dash display.

Also if you put the car in sports mode does it still do it?

I had a 3.0TDI cab s-tronic but cant say i ever experianced this issue.

My guess would be at some issue/feature of the mechatronic unit. i would suggest a reset of the ECU for the car to unlearn that potential behaviour. I'm not sure how much you need to reset for the mechatronic unit to reset too.
 

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I have a 2009 3.0 TDI tiptronic and I've noticed this, only in 3rd gear and at low revs. In D it will shift from 2nd to 3rd at around 1800rpm and when in 3rd the revs hang at 1800rpm for a few seconds then they drop to 1200 rpm like there is a 3a and b gear, he he. I have just put it down to the torque converter using more revs to build a little more speed in that gear until it can engage a direct drive.

Unlike a direct drive gearbox, like DSG, the revs can increase/fluctuate without a direct increase in speed.

Just my thoughts!?
 

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I have a 2010 3.0tdi S Tropic.

I noticed a similar fluctuation with mine in regard to the RPM in the run up to discovering the mechatronic unit was shagged.

Hopefully you're not in the same boat tho!

The main symptoms of my experience with the mechatronic unit involved the car thumping into 1st/2nd gear in stop start traffic and low torque when reversing out of sloped driveway.

The unit was changed and everything resolved including the RPM quirk.
 

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Discussion Starter #16
Audi have got back to me and can't find anything wrong and have said it is the DPF doing a regen and is using more fuel to heat up the exhaust, not sure if I believe them but if its only once a week for a few seconds it doesn't bother me much
 

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Audi have got back to me and can't find anything wrong and have said it is the DPF doing a regen and is using more fuel to heat up the exhaust, not sure if I believe them but if its only once a week for a few seconds it doesn't bother me much
That doesn't sound right to me, when mine regens the idle revs just rise.
 

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Discussion Starter #18
I didn't believe them either but has now been checked at two different Audi branches and they both couldn't find anything wrong
 

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have you asked them to reset the mechatronic unit? might be learned behavior?
 

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Discussion Starter #20
Hi to update my old thread, I have now got rid of the vehicle as it was giving me more displeasure than pleasure. The below fault code wouldnt clear and is related to the mechatronics unit so this may be linked to the above issues I had.

00260 - Solenoid valve 2 (N89)
 
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