The new Audi A4 TDIe aims to mix luxury and sportiness with fuel efficiency.

Compromise is typically the name of the game for car buyers hankering after space and real-world fuel efficiency combined with a dose of sporty performance. Two outa three ain’t bad, right?

Now Audi says you can have it all with the greenest version yet of its A4 mid-size sedan, dubbed the 2.0 TDIe.

We’re testing the theory on the type of road trip that holidaying families might find themselves on: kicking off by wading through Adelaide’s morning peak hour and ending around seven hours and more than 500km later in outback Broken Hill.

The designated route is deficient of the type of roads that showcase sporting virtue, but no matter. Today’s trip is mostly about fuel; specifically, how much – or little – we’re going to use.

Along the way we’ll reinforce our opinion of the A4’s worth as an open-road tourer that pampers up to four occupants in comfortable and classy surroundings. We’ll arrive in the rural mining centre feeling fresh, courtesy of comfy and supportive leather seats and a generous equipment specification that includes cruise control, climate control, a 10-speaker audio system that includes full iPod integration, and automatic headlights and wipers.

The first order of the day is to get acquainted with the 2.0 TDIe’s headline act, a stop/start system that can shut off the engine when the car comes to a halt, saving fuel that is normally burnt when the car is idling. Adelaide’s brief but heavy peak hour provides ample opportunity, with plenty of traffic around to regularly hamper our progress.

Bring the A4 to a halt, slot the six-speed manual gearbox into neutral and remove your foot from the clutch. In most cases the engine switches itself off with a tiny but perceptible shudder, and sits idle and silent until the clutch is depressed. Then it springs back to life with a quick cough, and is typically ready for action before you can slot first gear and move your right foot from the brake to depress the accelerator.

It’s possible to deactivate the system by pressing a button in the centre console, but with a system that works this well, why bother? Other irregular activities will also cause it to shut down – stalling, for instance. To re-boot the system, though, you need to reactivate the dash-mounted key with two presses, rather than simply stabbing the more conveniently located engine starter button on the console. It’s a small blight on an otherwise well-devised design.

There’s also an automatic over-ride function that will prioritise the car’s needs – maintaining the climate control temperature or feeding other demands on the electrical system – by restarting the stopped engine if needed.

Hand-in-glove with the stop-start system is another cornerstone technology, Audi’s “Driver Efficiency Program”. It has the dual role of informing the driver what the car is doing, and telling them how to drive more efficiently. Opening a window while the climate control is working earns a rebuke, while holding a gear for too long also prompts a suggestion that you should be paying more attention to the gearshift indicator.

You can also view your instant and average fuel consumption on the same screen, quickly teaching you where you use most fuel. It becomes an involving challenge to try to undercut the average by moderating bursts of acceleration and coasting more frequently to squeeze more distance from the fuel tank.

Another handy gauge shows how much your ancillary functions – such as climate control – are contributing to fuel use, although it requires some mathematical nous to recalculate the litres-per-hour readout into the standard litres-per-100km measure.

Other fuel-saving technogies are not as obvious, but still apparent in day-to-day driving. Aerodynamic measures including a 15mm-lower ride height courtesy of sports-tuned suspension help the A4 to scythe more efficiently through the air and generate better balance and handling, but also produce a less forgiving ride with small-to-medium road acne transferred faithfully through the cabin. Low rolling-resistance tyres generate significant tyre noise on coarse-chip surfaces, but gear ratios reconfigured for fuel economy do little to dampen the A4’s enthusiastic response to requests for acceleration. Brake energy recovery and regeneration is seamless and unnoticeable.

At the heart of it all is Audi’s 2.0-litre four-cylinder turbo diesel (or TDI, in Audi-speak) engine. With just 100kW of power but 320Nm of torque it’s flexible and willing, with equal enthusiasm for overtaking on the open road as for diving into a gap in traffic. The six-speed manual is relatively easy to use with a nice, positive clutch action but the lack of an automatic option – for which Audi is still working on a stop/start system – won’t overjoy some prospective customers.

So does it all make a difference to consumption? Or is it all metaphoric smoke and mirrors? Officially, the A4 2.0 TDIe gets a combined consumption figure of 4.8 litres per 100km, one litre per 100km better than the A4 2.0 TDI on which it is based.

In peak hour traffic, where cars normally drink the most, we saw around 3.0L/100km courtesy of frequent engine shutdowns, rising to 3.9L/100km by the time we reached the city limits as speed rose and traffic lights thinned. A couple more hours of highway driving nudged the average to 4.9L/100km by our lunch stop in the Clare Valley.

With trip computers reset we again hit the highway after lunch and with the stop/start system rendered redundant, consumption settled around the high fives, showing 5.7L/100km as we rolled into Broken Hill. Above the official average it may be, but we’d also rate it an above-average result relative to the comfort, space and ambience we’d enjoyed over the day.

Priced from $49,900 (plus on-road and dealer costs), the Audi A4 2.0 TDIe is the new starting point in the A4 range and undercuts its diesel-powered BMW and Mercedes-Benz competitors by more than $10,000 on price, and at least 0.6L/100km on official consumption.

Audi says it wants to woo hybrid drivers looking for more performance and sportiness. Although we’re yet to be convinced that the A4’s firmer ride will impress the conservative petrol-electric crowd, the A4 2.0 TDIe still ticks a lot of boxes.