A6 BiTDI - Idle Revs

[hshah]

I've been noticing a few odd things with my nearly 3 year old BiTDI... one of them being straight idle revs and the car juddering. A couple of days ago it was the worst it has ever been:



(the jump in revs at the end is me hitting the accelerator)


I am going to get my car booked it and get it sorted before the warranty is over, but I am just curious as to what could cause this?


I have also noticed that the car isn't as powerful as it used to be, definitely less fuel efficient and then you have my other thread regarding it regularly going into limp mode (link here).

Could all this be related in some way?

[A6S]

Maybe a Vacuum leak somewhere or maf sensor

[Elansear]

Hi. As it is pulsing then maybe an injector. Are you still getting DPF /LIMP problems ? If so then would suspect a strong link between them. Again I would think injection issue.

[hshah]

So, the went in yesterday and Audi called a little while ago. They claim that no fault codes are found and that that system would show any issues. I asked how extensive the error reporting / logging was because if they swear by it then I will not be satisfied until they explain to me the behaviour I reported (backed with video evidence). If they cannot explain that then the fault logging is obviously not good enough and I want it all confirmed in writing.

[A6S]

They plugged it in and computer says nothing wrong. That’s about the extent of the diagnostic maybe an extended test drive so the tech could grab his lunch
There’s not proper diagnostic nowadays. There’s too much reliance on the computer.
To be fare intermittent faults are difficult to diagnose and if they don’t take the time and rely too much on that expensive Audi computer then they won’t find much. Also being a warranty job they are not gonna spend too much time as they don’t get paid till something is properly wrong.

[hshah]

Haha, very true. My work is all about computer software / systems and I know I push back issues unless I have screenshots etc. I took the video to post here but also as evidence for Audi. Given that I have proof of something not right they have no leg to stand on when they say there are no fault codes, because they would be stating that those revs at idle are normal. If they are not normal then they would be admitting to the fault reporting not being as extensive. Either way I'm right and they are not. I said I would be happy to ignore the issue and take the car back if their master technician would give me a report explaining why this was occurring and that there was nothing to worry about.

I kind of feel sorry for the guy in between because I understand that he can only go by what he is told from their technicians and then you have me on the other end, ripping the reasons to shreds. One thing he did say was "you drive the car every day and you know it better than we do", which basically says that I know when something is not right and the lack of fault codes means nothing.

Seriously though, trying to explain to me that the DPF light is all about needing a regen and down to my driving style... I know how I drive and the car is behaving very very differently to how it was in the first 1.5 years. That is either normal and if so I want that in writing, or there is something wrong which they need to fix.

[A6S]

Just because there’s no fault codes doesn’t means nothing is wrong. Don’t know how many times I’ve explained that to the techs at dealerships. No fault codes means the parts are working to within normal parameters doesn’t mean it’s not faulty.
Easy way is to think about is a temperature sensor works between let’s say -20 to 150 degrees Celsius. As long as that sensor is between those values it’s doesnt log a fault. The thing is the sensor could be reading 100 degrees when in fact it’s only 10. Computer doesn’t see the fault even though the sensor is faulty. That’s the diagnostic bit that these techs don’t do like check with a thermometer and rely solely on that computer to tell them.

[hshah]

Completely agree, which is why when I said I wanted them to put in writing explaining that the idle revs and everything else I had said was normal, my car is now being kept in for another day. I can only assume the internal conversation went something like "Ahh crap, is the video definitely of his car? He wants what? In writing? Argh, this is going to take some time then, because we now have to check everything".

Because I had put the video on YouTube, they asked me a few times if it was my car. I had taken two videos... one for uploading and linking to on here with the mileage etc cut off and one without. I also sent them a screenshot of YouTube to show I uploaded it.

I'm not sure why they thought it would be a good idea to tell me that the system is really good and that any issue would be logged. Since the revs thing is not logged, either a) the system is not good or b) it's normal behaviour.

[A6S]

They are not gonna write a letter saying it’s normal. That’s like signing your own death warrant 😄
If you break down with and have a letter they will be looking at a court case, worse you go to the press.
The video bit I can understand. How many people would google a symptom and turn up and say my car is doing the same thing without actual evidence of it.

[RhysoTDI]

I had similar symptoms with my 3.0TDI a couple of months ago. It eventually got worse to a point where it would almost stall when stationary. No 1 injector failed but up until that point there were no fault codes

however, when logged in VCDS you could clearly see the injection values were way above spec

it was also accompanied by a hissing sound that was ever present as a result of the injector seal having perished

I’d ask the dealer to log the injector values; that will take them about a minute to see if an injector is at fault