IT'S taken nearly 4,000 miles to reveal the real benefits of the Audi's 2.5-litre TDI engine. As a believer in mechanical sympathy and a proper running-in procedure, that's how long I gave the Audi before exploiting its full potential.

And what potential. With 180bhp — and a thumping 273lb-ft of torque at 1,500-2,500rpm — the Audi is a real flyer. With its top speed of 140mph and 0-62mph acceleration time of just 8.6 seconds, it's got enough performance to see off most rivals — and many petrol equivalents besides.

To put it into perspective, the TDI's torque figure is substantially greater than the 3.0 petrol model's 221lb-ft at 3,200rpm. Even if its outright power can't compete with the 3.0's 220bhp, it's this torque that really counts in the TDI's favour. All who have driven the TDI have remarked how quick it is, and with its delightful short-throw six-speed sports gearbox, quick driving is both easy and rewarding.

Of course, the added bonus is that fuel consumption bears no relation to the 3.0's: combined consumption is 35.8mpg, compared with the 3.0's 26.9mpg, and I have seen the running-in consumption of our car improve from 32.5mpg to 35.4mpg, despite progressively harder driving.

For me too, the V6 TDI's gruff, throaty roar is one of the best diesel sounds around, especially with the subtly audible turbo whistle adding to the sound effects. It's enough to make you lower the side window when driving through town.

Owners of the previous Audi A4 will have been familiar with that car's notoriously light steering, sharp brakes and mildly ponderous handling, so it's excellent to report that the new car all but banishes these criticisms. In fact, in Sport spec, it is a positively rewarding driver's car.

Contrary to other reports that have criticised the A4's hard ride, I reckon Audi has achieved a fine ride/handling balance — but then I like a firmer suspension set-up. In practice, it is far preferable to the wallowing, slightly unbalanced feel you get in a non-Sport Volkswagen Passat, for example.

Even fast motorway undulations, which would have many rival models struggling for composure, leave the Audi unfazed and rock-solid. In turn, this inspires enormous confidence, particularly as the brakes are among the most reassuring of any car in the class. Firm, progressive and powerful, you can feel the electronic brake force distribution working hard on, for instance, a gravel-covered road under heavyish braking.

Words of warning to those contemplating ordering a new A4: the Sport does not have heated door mirrors as standard, and neither is there a trip computer — infuriating when trying to calculate average consumption. These options — which I am assured will be remedied at the 2002 model-year specification reviews — would cost £110 for the heated mirrors and £300 for the computer.

We also specified our car with electric front seats, an £800 option. Closer inspection of the options list revealed that the £1,420 'Comfort Pack' brings electric front seats (driver's with memory), electric lumbar support, automatic dipping rear view mirror, automatic dipping, folding and heated door mirrors with memory and heated windscreen washers.

But these are small gripes in a car that infinitely impresses in its build-quality, dynamics and comfort, understated class and, let's face it, sheer ownership appeal. Coupled with the A4 2.5 TDI's tax cost advantage — which will save a 40% tax-payer over £700 a year under the new regime — it's a convincing argument for Audi.