ajg617

This one was a bit troubling. I'm on my way to work this morning and as I'm coasting down a hill (local about 30mph) I see the tach bouncing 200-300RPMs continuously and it feels like brakes (or worse torque converter vanes) are cycling. Put it in neutral, and tach is steady and symptoms gone. Put it back in drive, and voila, tach starts jumping rhythmically and the whole car 'feels' like it is slowing each time the RPMs drop. No problem straight and level. No codes. Am going to have the fluid changed, but I did have the converter go on my 03 A6 but it didn't act like that.
TIA,
AJG

newa6er

there are several threads addressing this issue

eazy211187

Sound like your torque is done.

ajg617

That's what I would have thought but I called a ZF authorized center nearby and he said a faulty torque converter was unlikely and hinted at some shift programming issues. I also mentioned that I didn't experience this until after I had performed a throttle adaptation the night before. Re-learning was his vote after that, so we'll see. I know on my C5 that I got codes when this happened - no codes on this so far.

SchwarzS6

As you have probably seen in the posts if you have searched the archives I had this same problem. Tried to find it for quite some time. I cleaned and adapted the throttle body, had a carbon clean. Visited a local ZF shop in Connecticut. The two things I did not do were to change the Tranny fluid and change the torque converter. I got tired of the problem and traded the car for an '08. About the time I traded it Hoffman Audi in CT ran into the same problem at their other shop and resolved it by replacing the TC. Of course replacing the TC also does a fluid replacement.

After all of the diagnosis it is obvious that the TC is not locking up properly because the problem is occurring right at the time of the lockup. Unfortunately the tranny does not through a code for this for some reason.

Interestingly, the only complaints on the forum have been 2005 and 2006 model year cars. In 2007 Audi changed to a different fluid and changed the TCM programming. These changes can be done on your car but I do not know the cost. I would guess it to be about $800-$1000.

Good luck and let us know what you find.

odoboyusa

If it only happens on a hill, I'll bet it's your fluid level.
I had the same issue and it drove me insane, the rpm jumps were so quick that they barely registered in the vag-com logging.

What's happening is that for a split second your trans goes into neutral due to lack of pressure. It should happen mostly in the higher gears, after the torque converter is pressurized (using more fluid) and mostly at high rpms.

You might have a very minor trans leak and these transmissions are VERY sensitive to fluid level.

In my case, I was 250 ml low on fluid and that was the problem.

Keep us posted.

ajg617

I'm hoping fluid level is the case. It only happens down hill and when cold. Drove home tonight (50 miles) and went down the same roads. Not a hint of any problem. I'm toying with changing the fluid but dealer won't do it and ZF shop and my independent don't advise it either. That's really contrary to most of the posts I've seen here. I have a call in to ZF directly to confirm. If I have to, I'll change it myself but am really surprised at the response. Both the ZF shop and my indy say it was a different story with the C5 which clearly had a design issue. This one is pretty solid and I shouldn't mess. Very confusing.

odoboyusa

Having your indy check the fluid level and maybe top off with the same fluid can't hurt.
Maybe when they check the level, they can drain just a bit of fluid to look at it and determine its condition.
I have a 3.2 trans with 161k miles and it runs great so the 6hps seem to be a bit better that the C5 ones (5hp).