Buying a used Audi A4 can be a good path to acquiring a high performance luxury vehicle with minimal cost. However, you should be aware of the expenses that you may face after you purchase your car. Audi parts are not particularly expensive, but labor generally is and shops that will work on an Audi are not as common. You will need to think about the common problems and typical expenses that will tend to show up, such as timing belts, oil sludge, and ignition coils, as well as modifications you may want to consider, such as superchargers and chip upgrades.
$700: Timing Belt
Older used Audi A4s, primarily the ones before the year 2000, have badly designed timing belts on them that tend to give out earlier than normal. This will need to be replaced at the 50K mile mark, well before it breaks. A broken timing belt can result in serious engine damage.
$30: Oil Sludge
This too can cause engine damage. Oil sludge is when water gets into the oil and causes gelatinous mass, which clogs up the engine. Using synthetic oil and doing frequent changes can help to avoid this problem. In addition, sludge is more of a problem on the 1.8T than the 2.8.
$150: Ignition Coils
Again more of a problem on the 1.8T than the 2.8,, ignition coils tend to go bad frequently leading to rough idling.
$3000: Convertible Roof Replacement
Windows sometimes spring leaks on the convertible A4s. These are difficult to glue back on your own, depending on the weather where you live, and so often an entire roof replacement is the only long term solution.
If you have a 2.8 A4, the only way to get good horsepower out of it is to install a supercharger. The PES G2 is a good brand for the older A4s, and will give you around 300 horsepower.
Another good way to increase the power and efficiency of your A4 is to replace the engine control unit, which controls fuel flow and timing. This can also be upgraded to different software depending your needs.
Always keep an extra grand or two on hand on top of what you expect to pay when you buy a used Audi. Of the high end used automobiles, Audi A4s tend to be a good choice. With a little light modding, as well as regular maintenance, you can end up with a great vehicle for a good price.