The ALCO Filters MD9090 air filter is designed to supply air to the engine and is suitable for the Audi A6 Avant 4B5, Audi A6 quattro, Audi S6 quattro, and Citroen C5. It fits 1.8 quattro 1,781 cc engines with 92 kW of power, 1.9 TDI 1,896 cc engines with 81 kW of power, and S6 quattro 4,172 cc engines with 250 kW of power, for model years 1999–2005.
- Type: Engine air filter
- Compatibility: Audi A6 Avant 4B5, Audi A6, Audi Quattro, Audi S6, Citroen C5
- Height: 57 mm
- Length: 260 mm
- Width: 214 mm
- Engines: 1.8 quattro 1,781 cc, 92 kW; 1.9 TDI 1,896 cc, 81 kW; S6 quattro 4,172 cc, 250 kW
- Model years: 1999–2005
- Equivalent codes: GMC 90220970, OPEL 834285, HENGST FILTER E206L, KNECHT LX448, KNECHT LX622, MANN-FILTER C261682, MANN-FILTER C26168, PURFLUX A941