I recently bought a 2004 A6 2.7T S-Line with 74000 miles. Since I bought the car a month ago, the car has some acceleration problems. I've put about 1k miles on the car.
The car feels as if it is starting in 2nd gear. It has little to no power up to about 20-25 mph. But after those speeds my power is all there.
Also, the center dash where it shows what gear I'm in(automatic btw) becomes inverted. It also won't let me go into manual gear selection, or sport.

I already have an appointment with a local dealership to get my timing belt changed, so I'll have the problem figured out then. Just trying to see what the damage is before I take it in.

I do know the car has had an electrical system replacement, and driveshaft replacement done. Timing was done at 44k. All service done at Audi dealerships.
This car was very well taken care off, all service required was done.

 

sounds to me like your transmission is intermittently going into limp mode. could be something simple like fluid or.....

most likely fluid or a sensor. do a search for limp mode and I'm sure you will find a ton of information, some good, some not so much. good luck. keep us informed.

 

It's hard to diagnosis with that info. When you reach the speeds where it gains most of its power (20 -25mph) again, does it proceed to shift through the gears? Why would you be getting the timing belt changed after 30 some thousand miles? Kind of early, I believe the recommended mileage is 60k, no? You could have a combination of issues or it could be the intermittent limp mode as already mentioned. It has been my experience that an intermittent limp mode would not have stayed intermittent for very long. It sounds like you could have a vacuum leak as well as some other transmission issue. Is there any CEL's?

 

The recommended interval for the TB is 105,000 miles. Most people change it early, at 75,000 or so, as an insurance measure. Unless you have some oil leaks to take care of, I would put off the TB until you resolve the transmission issue because you may need a new transmission and you may decide that it isn't worth it.

Have the dealership check the fluid level and the TCU. These are common, easily solved issues affecting the transmission. Otherwise, you could have a bad torque convertor or other transmission internal problem which will get pricey.

Good luck,

Bob