Hi all, I have done some searching on this subject and could not find anything.

I have a 1997 A4 2.7 12V Quattro with a 5 speed manual 140k miles. While driving sometimes (with no pattern) the car will all of a sudden have bad acceleration and can't even maintain highway speed (65 mph). It feels as if I am trying to drive with the E-brake partially on. There is no CEL or pending codes and the engine sounds normal, just under a heavy load. FYI I just replaced the serpentine belt, but I am pretty sure that has nothing to do with it.

So first theory:

The front brakes seem a little hot after I get out, but as far as I can tell they are not dragging while I am driving (no sounds or grinding noise). I put the car in the air and spun the front wheels and they feel normal (although there is now a warped right front rotor with uneven pad wear). Could the master cylinder vacuum diaphragm valve be shot and have have the brakes partially engaged just sometimes? Any ideas how to test this?

Second theory:

There is a shiny spot of an oily substance right behind the end of the chassis heat shield right after the cats. When I went to touch it, it did not feel greasy and was actually pretty dry. There is no leaks from the rear seal on the center diff that I can tell. I did have my clutch line explode a year ago, so it could just be fluid left over. On the other hand when I shut down the engine I get a burning rubber smell when I step out of the car. Could the transmission/center diff be low on fluid and be burning itself up slowly putting a load on the engine? Although this would not explain the random event of this happening. I attached two pictures to try and explain this better.

http://dl.dropbox.com/u/40458536/photo1.jpg
http://dl.dropbox.com/u/40458536/photo%202.JPG

Last theory (most unlikely):

I overfilled the steering fluid slightly and get a whining sound when I turn the wheels to full lock. Could this have damaged anything in the pump and be loading down the engine?


Sorry about the novel, I just wanted to be thorough to give everyone the best chance of helping me out.