Faults:

Throttle body boot tore. Common issue, $40 and a half hour to replace (if left torn this will destroy the turbochargers).

Rear wheel bearing. $35 for bearing, $50 for pressing, took about six hours.

Coolant temperature sensor. $55 for OEM part. An hour to replace.

EGT sensor failure (passenger side). Jumpered bad sensor signal wire into good sensor output. About an hour of work.

Primary driver's side O2 sensor failure. Yet to replace, likely $80 and an afternoon.

General Comments:

Many of the reviews on this site for this car are from long ago, when the car was still newer. Some even mention dealer servicing. Well, it is a different time now. It needs to be viewed from a different perspective.

The B5 S4 is still considered one of the higher-performance cars on the road today. It is an incredibly complex car for its time, and even compared against today's vehicles is quite a technological showpiece. My friend, the previous owner, says it has "max everything: max turbos, max gears, max drive wheels, max power." He is, of course, referring to it against its contemporaries. In the early-mid 2000s, this was a car all the turbo tuning people talked about, regardless of their prejudices.

The performance, especially straight line, is phenomenal. The tuning potential is very high, and you will find very few unmodified cars since a simple chip/computer flash can get you almost 100 lb/ft more torque from the engine. The handling, unless you invest in a high-end suspension system (Bilstein PSS9 and above), is not even close to a serious sports car, à la BMW M3, Porsche 911, Mazda RX-7TT. It's fairly heavy -- it has poor weight distribution with a gigantor engine mostly ahead of the front axle -- and it feels like it. Even then, you will find most former or current owners of this car who have also owned or do own "serious" sports cars still say they love the B5 S4; that it's just "different." It is really a pleasure to drive on a day-to-day basis. It makes you feel like king of the road with the grip and hilarious torque wave. The handling isn't bad, either. It just doesn't deliver precision when you're at the limit. In the snow it is typical Audi awesome.

That said, it requires a special breed of car person to not have a horrible experience owning one of these, now 15 years since the end of their production. Here is the question I put to those considering buying one: if an intake hose tore and blew off while driving, would you understand the problem immediately and consider this a roadside repair, or would you have it towed to a shop to diagnose and fix? This car is for the first type -- the guy that hears a small noise and immediately begins running through the possibilities of what it could be. These are very sophisticated; a small boost or coolant leak could easily cascade into a blown turbo or cracked head respectively, both of which require engine removal and thousands of dollars just in parts. You'll always have a mental list of future repairs in order of priority.

I won't get into all the things that can go wrong on this car. The list is long, well established in forums and buyer's guides, and some items are very expensive. The most common major failure as these get up in mileage are the turbochargers. Anything that places additional stress on them will hasten their demise: chipping/flashing, boost leaks, infrequent oil changes, not allowing warm up and cool down, wailing on them constantly. Some turbos make it to 200,000 miles. Not usually "enthusiast" driven cars. Expect, in parts, $2000 minimum to replace them, $3000+ if you want to upgrade to a more durable (and powerful) factory type, and the engine must be removed for any turbocharger service. This can be a very intimidating project for a novice, and one that even some non-enthusiast mechanics will balk at simply because they don't want to deal with the agony.

That all out of the way, this is a very unique, very awesome-to-drive car. The fuel mileage sucks. The boost comes on fast, and you'll be laughing every time you blow away a 996 on the freeway. Don't let forum horror stories scare you -- this is one of the most rewarding cars to own, period. No, it's not a Honda, but it is still just a car.

Faults:

- Both pre-cat oxygen sensors needed repairing when I purchased it.

- Water pump impeller had broken, causing a massive coolant leak.

- Valve gaskets leak oil very slightly, causing a burning oil smell.

- One of the rear deck Bose speakers had blown. Passenger side door panel tweeter blown as well.

- Coolant temperature sensor went bad.

- Front passenger CV axle (replaced both).

- Front driver's side tie rod (replaced both).

- Some squeaks were coming from the upper control arms, so I went and replaced all of the front control arms (upper and lower) while I was replacing the CVs and tie rods.

- Rear driver window regulator or motor went bad.

- Had the infamous P-0741 Torque Converter Clutch stuck off; I tried replacing the lifetime filter and fluid, and this did not help.

- Unsure if it was ultimately the converter clutch or something else, but the automatic/Tiptronic transmission ultimately began slipping 1-3rd gears so badly that the car became nearly un-driveable, so I traded it in.

General Comments:

Excellent car for tuning and modifying! There is a very strong enthusiast tuner community for this car; lots of options for how to upgrade and modify, and the costs for such an upgrade are getting more and more reasonable. For example, a Stage 3 Frankenturbos setup can yield 400+ AWHP for $4-7k, and allow 0-60 in less than 3 seconds. Or if you don't want anything that extreme, a $500 chip can get you to about 310 bhp and 370 lb ft of torque; no other car can give you that kind of increase in power for so little.

There are lots of costly maintenance jobs and repairs mandatory for this model. It is highly documented and well-known among the community that there are issues like control arms, which fail after 50k-100k miles, and it's not uncommon for an owner to change them 3 times within his/her ownership. The water pump is horrendous, as are the 30V valve leaks, so you can expect to be paying $1500 every 75k miles to get the timing belt/water pump/gaskets replaced. The transmission seems to be the really aggravating part -- Tiptronics suffer from a horrible torque converter that will hit you at one point or another, and the manuals have a 1-2 gear issue as well.

Everything aside, the performance is good. Torque delivery comes early, and if you floor it, you won't feel like you're going very fast because of the smoothness, but if you look at the speedo, you can tell you are. The car is very pudgy though, coming in at 3700lbs, and you can feel it at times.

I don't like the seats. I feel like for an S model, they ought to be sportier, and not designed for a 300lb man.

The interior is nice, and can look outright sexy with a Nogaro blue interior.

The exterior is very sleeper-esque, and drops subtle hints that the car is not a typical A4, which is nice, because you won't attract much attention.