The.aviator2

I was searching the last couple of days about what would cause the rpm to bounce at low rpm range but stay solid at idle and been getting results indicating transmisaion's torque converter problems.

That could be just a coincidence. However, I was driving on the highway today and decided to shift to S and floored the pedal. Everything was normal until it was coming towards redline on 5th gear and transmission decided to shift to 4th instead of going to 6th. The rpm went in the REDLINE range and was hitting the limiter. I eased up on the throttle and manually shifted to 6th and it did. After another minute, I gave it another go and the same thing happened, car shifted to 4th and not 6th.

can someone help with an explaination to what would cause this to happen?

Thank you,

The.aviator2

bump for help.

mishar

Could it be that your 6th gear clutches are sliding when shifting under power?

RobertV

How many miles on the S8?
Do you have any service history?
How long have you owned it?
Have you had it scanned at an Audi dealer or do you have access to Ross Tech VCDS?

If it were mine my first step would be to get it scanned and inspect the fluid.
Dependent on what was found I'd likely change the fluid to Redline with a new filter and gasket.

Jack88

I'm with Robert, get a VCDS scan. The only way I know to get eyes on your fluid is to change it, so if you haven't done that before or it's been a long time, may as well do it anyway as you're due. Low fluid level can cause the RPM fluctuations you noted. The gear change issue could have the same cause, but you should know it's pretty rare that anyone gets their S8 up to the kind of speeds required to shift to 6th at high rpm, so it's conceivable that no one else encountered that symptom even though it would have been present.

mishar

Jack just pointed, what speed was that? 270 km/h?

target39

"Flooring the pedal" activates the kickdown switch, which is supposed to downshift to allow you to accelerate more. You should be able to feel the switch actuation point when you push the throttle pedal down all the way. At the point before actuation is technically 100% throttle, any further (pedal to the metal) actuates the kickdown switch and tells the car to downshift.

The.aviator2

I should've mentioned...yes, I scanned the car afterwards and no fault found in the module.

Being hesitant and thinking "if it isn't broken don't fix it", I've postponed the transmission service even though I have purchased the filter and the pan gasket a month ago. I don't believe the car ever got any service for the transmission. It's showing 125k km (approx. 78k miles).

The.aviator2

I read about the switch but I also have turned it off a while ago. What happened to me on the highway was totally not normal to the point where I had to think for a period of time to realize that the car actually did a downshift instead of an upshift!

The.aviator2

I can't recall the actual speed at that time (not 270kph for sure). My daily commute to work is on a rural highway where it's mostly empty in the early morning. It gets a bit boring sometimes

I think the first thing to do now is ATF change + filter.