Guilty as charged, I'm afraid. When I first heard that Saab were endowing their 9-3 Convertible with a 1.9-litre diesel engine, I thought it would be a peaky little thing, all turbo lag and lunge and no flexibility. Putting an engine with this modest capacity into such a hefty drop top surely was a recipe for a dull and stodgy driving experience? I'm glad to report that I was wrong. This is a convertible with a surprising amount of get up and go.

Those with an eye on the global automotive industry will know that Saab have been working with Fiat on diesel technology and the products of this development cycle are manufactured at the FMA plant in Italy. Saab have access to three powerplants, a 120bhp 8-valve unit, a gutsy 150bhp 16-valver and the 180bhp version with its two stage turbocharger. Thankfully they've resisted the temptation to put the modestly powered 120bhp unit into the Convertible and rely upon the two punchier engines instead.

Here we concentrate on the 150bhp unit that's priced from £26,430 in entry-level Linear SE trim. This 1.9-litre unit replaced the 2.2-litre TiD engine that the current generation 9-3 had from launch, Trollhattan's first ever diesel. Four years hard development work went into that engine and it was a decent effort but despite continual improvements, it was never capable of matching the class best in terms of emissions and fuel economy. This 150bhp 1.9-litre TiD unit addresses those concerns very effectively.

Mated to a six-speed manual gearbox as standard, with the option of a six-speed auto, there's plenty of scope for plugging the car straight into the meat of the torque curve. With at least 90% of peak torque available in a broad load running from 1,750 to 3,250rpm, you'll be guaranteed respectable progress.

"Somewhat against the odds, this 1.9-litre turbodiesel engine makes a very accomplished partner to the 9-3 Convertible"

Compared to the old 2.2-litre TiD unit, the 150bhp 1.9-litre TiD generates 20 per cent more power with the added benefits of lower CO2 emissions and better fuel economy. Importantly in a soft top car, it also offers significantly better refinement. Saab have worked closely with turbocharger manufacturer Garrett to optimise the performance of this low inertia turbocharger and the result is very close to that target for all decent turbocharged cars, namely to feel like a normally aspirated bigger capacity engine. The variable geometry vanes in the turbo unit allow the pitch of the blades to be electronically adjusted for strong low-end torque and then tuned to offer a smooth transition into the turbo's power phase.

It's respectably quick too, punting the big-boned Convertible to 60mph in just 10 seconds but the in-gear acceleration times that really indicate a diesel engine's torque response have been slashed dramatically. Surging from 50 to 70mph in fifth gear - a typical A-road manoeuvre - takes just 8.7 seconds. This being Saab, the engine is clean too. You won't want to be choking on your own expulsions and the powertrain includes one of the most advanced diesel particulate filters on the market, enabling Euro IV emissions compliance - an essential requirement for many company car drivers. Unlike other particulate traps, it is maintenance-free and self-cleaning, requiring no additives or periodic replacement. In order to clean the filter and to keep the exhaust flow as free as possible, deposits are periodically burnt off by short pulses of over-fuelling. These briefly raise exhaust temperatures to the required level of 600º C. The process is automatically initiated when back pressure in the exhaust system reaches a certain level and is completely undetectable by the driver. The self-cleaning process takes place whenever necessary, irrespective of throttle load or engine temperature.

All the current Saab 9-3 Convertible models benefit from a facelift based on the Aero X concept car. The clamshell bonnet visually widens the front of the car and all external rubbing strips have been removed to give a cleaner look. There's a classier finish to the front grille and a set of LED light strips that sit across the top of the headlamp pod while the rear light clusters are shrouded in smoked glass. Inside, there's a more muted effect with less silver plastic.

When work began on this 9-3 Convertible, Saab's designers were determined to imbue it with the same handling characteristics as the acclaimed 9-3 Sports Saloon. In order to overcome the loss of rigidity caused by removing the roof, a secondary supplemental chassis was developed, effectively a ring of steel linking and reinforcing the front rear and side structures.

The result is a car devoid of the shake, rattle and roll of many convertibles. Of course, many drivers won't care a jot about chassis stiffness, but the result is a car that drives more smoothly, that allows its suspension to work properly and which also permits designers to work to fine tolerances in the construction of components like the electric folding hood.

The Saab's hood may not be of the trendy folding hard top variety, but for a ragtop it's very impressive. Electrically operated, it requires no unlatching or arcane procedures to operate, and retracts in just 20 seconds, making it possible to drop the top at traffic lights without the potential embarrassment of being caught at half mast when the lights turn green. The hood's operation is very slick indeed. Instead of flipping up, an aluminium tonneau cover raises itself and then slides back, making for a quicker operation and a better seal than a traditional hinged cover.

The 9-3 Convertible has consistently been one of the strongest-selling premium four-seater drop tops on the market. Endowed with this fine diesel powerplant, the likes of BMW, Volvo and Audi will only have an even tougher nut to crack.

TOP 4 9-3 DEALS

The results below show the top 9-3 deals on buyacar

	Saab 9-3 1.9 TiD 150 Vector Sport 2dr Convertible
	ETR	Mthly £459	Saving £4,988	Price £24,562
	Saab 9-3 1.9 TiD 150 Linear SE 2dr Convertible
	ETR	Mthly £432	Saving £3,865	Price £23,075
	Saab 9-3 1.9 TiD 150 Linear SE 2dr Auto Convertible
	ETR	Mthly £445	Saving £4,625	Price £23,730
	Saab 9-3 1.9 TiD 150 Vector Sport 2dr Auto Convertible
	ETR	Mthly £470	Saving £5,835	Price £25,130

typical 11.47% APR

PCP finance quote over 48 months,  10,000 miles pa,  deposit of £1000