In heavy traffic on the freeway, I let the 2014 Audi A7 TDI's cruise control handle braking and accelerating, and gave lane-keeping assist a try by letting the car drift over to the left lane line. Cruise control, using its radar to track the car ahead, unerringly handled stop-and-go without my intervention. And before the car crossed the lane line, the camera-based lane assist moved the wheel under my light grip, steering the A7 TDI back into its own lane.

Was I experiencing a glimpse of our autonomous driving future?

Not exactly, as the pull on the steering wheel sent the car on a drift toward the right lane line, from which it also corrected. If I let it have its way, I figured it would drunkenly weave back and forth between the lines, then get completely thrown off by the first serious curve or faded line paint. The A7 TDI's radar and cameras made it dimly aware of its surroundings, but true autonomy requires more sophisticated sensors.

Despite not exactly being the future of self-driving, the A7 has been a high-tech showcase for Audi since its launch in 2010, not to mention having an excellent body design that became much copied. For 2014, the A7 adds some driver assistance features, but its connected infotainment system is largely the same as before.

Double down on diesel

The big change for the 2014 model year, as indicated by this A7's TDI suffix, is the inclusion of a diesel engine option.

Over the last decade, Audi's parent company, the Volkswagen Group, developed drivetrain technologies ahead of the competition. The company was an early adopter of direct injection to improve engine efficiency, put quick-shifting dual-clutch transmissions into affordable performance cars, and maintained a line of diesel passenger cars as every other automaker steered clear. Audi benefited from this work, using direct-injection engines in every model and offering diesel versions of the A3 and Q7.

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For 2014, Audi doubles down on diesel, putting TDI, which means Turbocharged Direct Injection, in the A6, A7, A8, Q5, and Q7.

Like its siblings, the A7 TDI I tested was powered by a 3-liter V-6 engine, turbocharged and mated to an eight-speed automatic transmission. As is typical for diesels, the horsepower, 240 in the A7 TDI, looks small given the size of the engine, but torque, at 428 pound-feet, is through the roof. That's compared with a more balanced 310 horsepower and 325 pound-feet of torque for the gasoline-powered A7.

Given the high torque, you might think the A7 TDI would shred its tires at every start, but Audi's throttle programming lets the power come on smoothly for the most part, making the car an easy everyday driver. There are some quirks to driving this diesel. First of all, if you've got F1 aspirations go for the gasoline A7, or step up to the S7 or RS7 models. The diesel engine doesn't deliver power in a manner suitable for thrashing the turns.

Redline sits at 4,500rpm and, more importantly, peak torque hits in a narrow band, from 1,750 to 2,250rpm. The gasoline-engined A7 spreads its peak torque across a 1,600rpm power band. In practice, the A7 TDI didn't have a lot of punch to power out of a turn with. The engine was prone to surge, churning out uneven acceleration when I had the throttle down. In Dynamic mode, the surging nature of the engine even made holding a steady pace in traffic difficult.

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From the outside, the noise from the engine was remarkable enough that CNET's garage attendant asked me if there was something wrong with the car. However, Audi employs enough sound deadening to mask the engine noise in the cabin.

As with other new diesels, the A7 TDI requires a little extra maintenance over the gasoline version. Every 10,000 miles, it needs a refill of its AdBlue tank. The emissions system sprays the AdBlue fluid into the exhaust stream, where it breaks down nitrogen oxide into its component parts.

Long-range driver

Given the power delivery, noise, and extra maintenance, you might be wondering why Audi would bother with diesel at all. Fuel economy is the key here, as the diesel drivetrain in the A7 TDI gives it an EPA-rated 24 mpg city and 38 mpg highway. Audi claims a 650-mile range from the 19-gallon fuel tank.

During my time with the car, the white LED lights indicating fuel level turned off at a glacial pace. At the end of a driving course involving city traffic, 65 mph freeways, and twisty mountain highways, the car turned in a healthy 30.3 mpg. Most drivers will likely average over 30 mpg.

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Contributing to the city fuel economy is an idle-stop feature, shutting down the engine at stop lights. Although there was no disguising the noise and vibration from the engine's stops and starts, I didn't find the feature hampered my driving. The engine started up readily whenever I lifted my foot from the brake pedal, and the system was smart enough to keep the engine running if it was cold out.

For those that find the A7 TDI's idle-stop too annoying, it can be turned off with the push of a button.

Although the A7 TDI is more of a luxury-efficient car than a sport play, it did handle very well. Quattro all-wheel drive comes standard on all A7s, and the suspension architecture is conducive to flat cornering. When I could keep the engine up in its power band, I could feel how Quattro helped the tires dig into the turns.

Audi's Drive Select feature let me choose from Comfort, Auto, and Dynamic drive modes, or configure a custom feel with its Individual setting. Those configurations included Dynamic settings for the engine and steering response, along with the seat belt tensioner and even adaptive cruise control.

However, even in Dynamic mode, the steering wheel feels light, a typical Audi characteristic. A strongly boosted electric power-steering system means the wheel turns very easily, although its precision varies somewhat depending on the Drive Select setting. At speed, the wheel gains some heft, helping maintain a straight line on the freeway, for example.

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Not available on the A7 TDI is Audi's Sport Differential, which dynamically vectors torque across the rear wheels to aid cornering, nor does it have an adaptive suspension. However, I found the suspension tuning was a nice compromise between comfort and handling.

Having eight gears in the transmission also helps the car's fuel economy, giving the engine more speeds where it can remain in its sweet spot. At freeway speeds, it let the engine turn at a leisurely 1,100rpm.

The transmission includes a Sport mode and let me shift manually, using the stick or paddles on the wheel. But even with Sport engaged, the gear changes felt slow when I attempted to hit the A7 TDI's specced 5.5-second zero-to-60 mph time. It didn't snap off particularly quick changes when I used the paddles, either. In everyday driving, however, the transmission worked without fuss, never seeming to hunt for gears.

Photographic evidence

I've written lovingly in the past of Audi's cabin electronics, and the A7 TDI is no slouch in this regard. It comes standard with the same Google Earth-integrated navigation system as prior models, showing maps in perspective or plan view. For more traditional-minded drivers, the maps can be viewed in a more graphical format, but I like seeing actual photographic evidence of the terrain through which I'm passing.

Google Earth relies on a built-in data connection in the car, which also powers Google local search. I've used this to search for lunch places while on the go, and found it better, and more legal, than trying to fumble with my iPhone at 65 mph on the freeway. When I entered any search term in the car, it returned a list of nearby businesses. More useful would be something like Yelp integration, which would come up with not only local businesses but ratings for restaurants and the like.

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The connected information services included in the A7 TDI are not well-known apps, but white-label weather, fuel, and location services. One useful new app Audi implemented showed me detailed parking information for garages in San Francisco, including hours, rates, and even space availability if the facility had the infrastructure to provide that information.

Whenever I set off in the A7 TDI, the infotainment system asked if I wanted to establish a data connection, which proved annoying time and time again. That might have been more of a press car problem, and I hope owners can do away with that prompt screen.

One area where a lot of automakers struggle is the cabin tech interface. Audi calls its the MMI, for multimedia interface. It consists of a central dial surrounded by four buttons, then four more buttons offering quick access to major functions such as navigation, audio, and phone. With familiarity, I've found that I don't need to look at the buttons to find the right function or menu.

The most impressive piece of this interface is the touch pad. Although only used for selecting radio presets, alphanumeric entry, and exploring the map, it is very cool technology. As I barreled down the freeway, I used it to enter a street address, tracing the letters for a street name. Its ability to recognize my crude tracings was near astounding.

Voice command is another option for entering addresses, placing phone calls, and controlling the stereo. It showed some good capabilities in the A7 TDI, such as letting me enter an address by saying the entire string at once. For selecting music, it was more limited, merely letting me ask for artists or albums from the onboard audio system.

This A7 TDI came optioned up with the Bang & Olufsen audio system, consisting of 15 speakers and 1,300 watts of amplification. I really like the sound from this system, finding it brings out elements of recordings that get squashed by inferior systems. However, low-bit-rate digital recordings sound terrible, as the system reveals all the flaws of compression.

Paving the way for a really awful audio source, Audi only includes a 30-pin iPhone connector for iOS integration. When I plugged in a Lightning adapter and my iPhone 5, the sound, coming through the cheap digital-analog converter in Apple's adapter, was atrocious. I wish Audi would include a standard USB port and let me plug any iOS device, or USB drive, directly into the car. From what I've been told, Audi merely plans on adding a Lightning cable adapter that will plug into the car's proprietary port.

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Bluetooth works for wireless audio streaming, but I had to access my phone to choose music. With a little Internet research, I figured out a way to stream music over the car's Wi-Fi connection from my iPhone. Android users can download the Audi Music Stream app to connect to the A7 TDI, and not only listen to music wirelessly over the car's Wi-Fi, but select music using the car's own interface.

For whatever reason, Audi has not released its Music Stream app for iOS in the US iTunes store. That app is available in other markets, so I created an account with the UK iTunes store, downloaded the free Audi Music Stream app, and installed it on my phone. The app opens up a world of music, not just that stored on my own iPhone, but a huge list of Internet-based radio stations from all over the world. Audi should be releasing a US version of its Music Stream app sometime next year with the launch of its new A3 model.

Best of many worlds

Those interested in a high-tech luxury sedan with exciting and practical body styling, and who also want excellent fuel economy, should definitely look toward the 2014 Audi A7 TDI. According to the EPA numbers, the A7 TDI boasts 8 mpg better, on average, than its gasoline counterpart. And for the majority of drivers, the few quirks of a diesel drivetrain will easily be accommodated. But as I pointed out above, those looking for an aggressive driving experience will have better options in the S7 and RS7.

The driver assistance features in the A7 TDI fall just short of the current cutting edge. The car can keep pace with traffic by itself and keep weary drivers from veering off into the weeds. Multiple camera views help avoid dents when parking, but there is no automated parking system, nor does the A7 TDI offer the kind of steering assist we saw in the Mercedes-Benz S550.

The cabin tech features are the A7 TDI's true glory, and Audi has shown it can build on its previous offerings, adding features such as the parking garage information app. However, Audi is currently not updating existing cars with new features. The built-in data connection is one of the best I've seen among production cars, and Audi uses it to feed interesting in-dash apps. I would like to see the sorts of apps I use every day on my phone integrated with the car.