guys, i know this is a very very old thread...but for the sake of anyone currently looking for a b5 s4 (like me), i found the following page quite helpful/good read:
http://www.strikeengine.com/audi-tuning/s4-tuning-buying-guide.html
and especially this part:
1. Boost leaks, not a problem in itself but they can lead to the turbos over speeding as they try and maintain the programmed pressure. Woo ooo like noises from the turbos can point to them needing changing in the not to distant future. Screaming sounds from the turbos will mean they are shot. It's 1200GBP plus VAT to change the turbos.
2. MAF sensor, if this fails the hotter exhaust gases can destroy the lambda and EGT sensors, 106 per side for the lambda and 139 for the EGT sensors. 80GBP for the MAF.
3. Recirculating boost valves, the diaphragm can fail leading to loss of boost and therefore power. S3 ones can be used as replacements as they are only 24GBP. Uprated valves are also available from Forge Motorsport.
These 3 faults can get by a Audi main dealer service as they don't trigger fault codes.
does anyone have anything to add to this? i too have around 5-6k to spend, but dont want to fall into the trap of buying a stinker of a car. anyone know of any other common faults or what to look out for when buying one of these STUNNING cars?
Cheers