I have a 2005 A6 4.2 (non SFI engine) what has recently started showing some strange behavior. Ever since i got the car it would have a slight surge when it was cold (usually sitting a few days undriven). When starting RPMs would go up and down about 100-200 RPM, would always go away after a short distance.

This week i was on the freeway doing about 70 and it started surging when i was driving, about 100 RPM or so, just enough to feel it when you are driving, I had the cruise on so I know it wasnt my foot doing it. The next day it was surging when driving 60, but it was accompanied by a vibration this time, seemed to be in sync with the surges; shifting down to 5th seemed to make the surging stop, along with the vibration. There is no vibration or surging when coasting or braking. I notice it will do it occasionally when shifting too.

When driving about 30 if you accelerate very slowly it will steadily vibrate, but if you accelerate harder it does not. I checked the MAF, air filter, engine oil, etc and have not found anything. There are no MIL indicators on, and no errors when connecting to the VAG-COM. I have found a few forums online that mention the torque converter was causing it, some say the valve body in the tranny, and some have replaced both and the problem remains. From what it is doing i was thinking it was a torque converter, but dont know for sure.

Has anyone had this issue and/or could provide some advice on what the source could be?

Thanks!

 

Torque converter is starting to go. I bet the ATF was never changed.

 

I have been told the ATF is a "lifetime fluid." I was planning on changing it out, but I only have 80k on the car.

Probably a little late to try just changing out the ATF, huh?

 

Just had the torque converter changed at a shop, the issue persists; the dealer said they test drove it without any issues, but as soon as I came to pick it up, it will shutter under light acceleration, identical to the issue i brought it in for. The shop said they would take care of it Monday, but I am a little upset because the torque converter appears to have been changed unnecessarily.

Very noticeable in 6th gear going up a slight incline; light throttle will result in a small engine RPM dip and a very noticeable shutter, feels like it is coming from somewhere in the drive line. Harder acceleration does not cause the issue. The shutter will repeat every 5 seconds or so and last about 1 second.

I'm trying to think of the very first time I noticed any weirdness, it was after I had a flat tire, I changed it to the spare (which is smaller then the other tires) and had one new tire replaced since there was only 1/32" of wear on the tires. I don't think the tire size difference would cause this, having a difference in air pressure or turning around a corner would make more of a difference then that.

Anyone have any suggestions or experience with this at all?

 

You mentioned you were driving on a smaller tire size for only 1 out of your 4 tires. For how long? I think to recall that Quatro is quiet sensitive when it comes to different sized tires on the same car. Is it possible you damaged the differential?
I'm no expert just throwing something into the room

 

I think its the clutch release bearing causing the issue.

 

It's an automatic, so the only clutches are inside of the Torque Converter, everything inside there should have been replaced when they rebuild the converter.

As for the tire size, I was still driving on the new tire when i brought it in to the shop. I would understand if the car had the issue all the time that it would be the tire size causing the issue, but as I mentioned it is only 1/32" difference, air pressure can make more of a size difference then that. Its not like one tire is a different size or anything. Although the spare in my car is a different size, it is a 245/40, the rest on my car are a 245/45; I guess it is possible something was damaged on the drive home before i had the new tire put on, but I had driven with that same spare 2 years ago when I had another tire that was damaged without any issues.

Just weird that it doesn’t always do it if there is something wrong with the diff. Hard acceleration will not show a RPM change or vibration; only light acceleration, especially noticeable when going uphill.

 

The shop changed the wheel s and tires, issue persists. They are getting no helpful information from the VAGCOM; and have been unable to find anything wrong with the car that would cause the vibration. It gets increasingly bad as you increase speed, especially light acceleration going uphill, seems to do it at any engine speed and in any gear at speed.

Their next step is to call ZF and see if there are any TSBs on the transmission.

Anyone have any ideas at all?

Thanks

 

Take a look in the transmission section of my private TSB library. Here is the link.
Audi A6 TSB List