Mazda has expanded its 929 luxury sedan lineup for 1990 with the addition of a new S model.

The S looks like the regular 929, but it acts differently thanks to adual overhead cam, 24-valve version of Mazda`s 3-liter 18-valve V-6 under the hood. The 24-valve develops 190 h.p. versus 158 h.p. on the 18-valve.

The 24-valve is potent when leaving the light or merging onto theexpressway but can loaf once at cruising speed. The four-speed automatic has achoice of three shift-point settings-economy for maximum mileage, power toboost acceleration and hold for low-gear ranges for greater control onslippery roadways.

We found in our test drive that pushing the power setting helped us tospring from the light and easily slip by in the passing lane when a littleextra power boost was needed. The beauty of the system is that the engine and transmission remain quiet when called on to perform.

The 24-valve delivers 18 miles per gallon city/22 m.p.g. highway,slightly less than the 19/23 rating with the 18-valve V-6.

The rear-wheel-drive S also features revised shock absorbers, springs and larger 15-inch radial tires to improve ride and handling. Front and rearantiroll bars minimize body lean in corners.

The 929 S also incorporates speed-sensitive power steering that variesthe amount of assist based on vehicle speed and steering-wheel angle. Atfaster speeds, there`s less assist, at slower speeds or when making low-speed parking maneuvers, the system offers more help.

Four-wheel disc brakes meant quick, true stopping. As insurance,especially in the Snow Belt, four-wheel antilock brakes are standard in the S,optional in the regular model.

The 929 S is built on a 106.7-inch wheelbase and is 193.9 inches longoverall, roughly the dimensions of a Ford Taurus. It tips the scales at 3,500 pounds, though the suspension and speed-sensitive steering give the impressionyou`re handling far less weight.

Trunk space is above average and rear-seat room and comfort isexceptional. The tops of the rear-seat backs form a semicircle for addedsupport and improved comfort.

But we were disappointed in the 929 S`s power front seat. The adjustmentnever felt just right. We wanted the seat bottom to go down more or the tiltsteering wheel to rise a bit higher but never got the two in sync. And theseat back seemed to rest just above the shoulder blades. We would have feltmore comfortable in long-distance driving if that back was about one inchhigher.

A couple of features are worth noting. The heat/air ducts have a``swing`` button you can push to have the hot or cold air continuouslydirected left to right so you don`t get too hot or too cold from a steadyblast of air.

And to help prevent unnecessary body damage, the bumpers, wheel wells and rocker panels are covered with a thick plastic protective molding.

But there were a few annoyances. The covered headlamp lenses a re modernand stylish, but they flank what looks like an old Buick Ciera grille. Agrilleless front end would be a nice touch.

The antilock braking system is standard as a safety measure. Theautomatic shoulder belt for the driver tends to slip on the shoulder. It needsjust a touch more tension to hold in place.

The AM/FM stereo with cassette in the test car had poor clarity and somesound distortion. We had to keep dialing up the sound level.

Other standard equipment includes power brakes and steering, powerwindows and door locks, leather-wrapped steering wheel, cruise control, power driver`s seat, power moonroof, air conditioning and AM/FM stereo withcassette.

The 929 S 4-door sedan starts at 24,800.