The air filter change interval is ludicrously long. Cars (1.4 TDi 70) third service at 19.5k and still not changed - its nearly three years old!

I bought one for £8 and did myself, and avarage mpg has risen from 50 (over 12 tanks) to 56 (after two entire tanks after the change)

It didn't look too dirty either....

A little trick with Vaseline.

Lightly smear around the air pipe connection edges (especially the air sensor in/out pipes) and filter to ensure a real good air tight seal.

JDW