Hi there i have a 1997 audi 2.5 tdi with 75000 miles and just the other day i was driving the car along the road and it sounds like there seems to be a loud like fan stuck on and the more you rev it the louder it gets.I use to have many 4x4 ford sierra,s 2.8 and i can recall fitting many viscus coupling,s fans to them.This noise i have on my audi is the same as that or a plane takin of which is noisy and then once it gets up in the sky it the engines backs of to become quiet again well my audi sounds like its keeps takin of or sounds like the choke is stuck on or could it be a sensor.Can anyone please help me it would be much appreciated.
Regards,
John Mann.