Cars don't need to have their engines running when they're stopped at red lights. That's why a number of automakers have developed start-stop systems, which stop a car's engine when the vehicle comes to a halt, and start it again as soon as the gas pedal is pressed. Bosch, however, is taking things farther. Its new start-stop system shuts the engine off not only at stops, but also whenever the car is coasting.
Putting it simply, the "start-stop system with coasting mode" turns off the engine whenever the vehicle can maintain its present speed by rolling. In other words, if the driver's foot isn't on the gas or brake pedals, the engine is off. A simple touch of either pedal causes the engine to instantly start back up.
According to Bosch, tests carried out by the company indicate that most vehicles could coast for about one third of every trip. If the engine was shut off for those periods, it would result in fuel savings of about 10 percent. Additionally, Bosch claims that if every new car sold in Germany were equipped with the system, "the theoretical annual reduction in CO2 would amount to over 30,000 metric tons" (33,069 tons).
What's more, with the engine off, the decreased mechanical resistance should allow cars to coast for longer distances than would otherwise be possible.
The system can reportedly be added to almost any type of existing combustion engine (including hybrids), and requires the installation of relatively few additional parts. It can even be added to cars with manual transmissions, if Bosch's eClutch is also used – this disengages the clutch whenever the vehicle is in coasting mode.
There's no word on availability or pricing of the system, although it is described as "affordable."
Source: Bosch
The engine continues turning without fuel, as long as the car is in-gear, the wheels turn the engine and alternator, so you still have power steering and brakes, electricity, everything, and the ECU starts sending fuel as soon as you touch the accelerator.
In many newer cars many of the ancillaries (including power steering) are electric. Therefore turning of the engine whilst driving doesn't affect these.
One thing which needs to be in place will be an electric brake booster (instead of vacuum powered boosters), though I assume (not familiar with the specifics) that in hybrid cars, and indeed other late model vehicles this already exists. (Or the brake circuit may be a high pressure, servo actuated system.)
http://www.drivingtesttips.biz/what-is-coasting.html
Plus, as James said, ECUs have been using fuel-cut on overrun for years so this is redundant. It's just a gimmick to sell even more starter motors!
As for de-clutching on the overrun, free-wheel systems have been around for ages. They have never really caught on, but who knows, perhaps they are due for a re-think, especially if only fitted to the top one or two ratios so that engine braking was still available if the brakes failed. That, of course, assumes that the driver would be capable of letting go of the steering wheel with one of his white knuckled hands in order to change to a lower gear as the car rolled ever faster down the hill it was on!
There are a number of reasons for this, where coasting is seen as a big no no. I also remember hearing topgear saying that you use no fuel at at all or next to nothing when you drive to a stop in gear, the cars wheels basically keeping the engine turning over as fuel is cut.
This technology would mean you could save fuel while coasting, but wouldn't save you any fuel compared to driving to a stop. Currently when you coast the engine has to keep itself ticking over instead of the wheels keeping it ticking over, so the engine could cut off.
But instead, just learn to drive properly, and drive to a stop, "coasting" in gear. Although it would be interesting to see how much people actually coast and how much could be saved.