The first Q45 came to market in 1989 as 1990 model. Car magazines and reviewers were impressed by the Q45's performance such as a 0-60 mph acceleration time of 6.7 seconds, and its high-output 4.5 L V8 engine rated at 278hp (207kW) and 292lb·ft (396N·m) of torque though many enthusiasts often claim a true power rating of over 300hp (224kW). At the time, its targeted competitors such as the Mercedes S-Class, BMW 7 Series, Jaguar XJ and Cadillac Fleetwood had much bigger engines with horsepower ratings in the lower 200hp (150kW) range and 0-60 mph times at an average of 10-11 seconds. All Q45s include a VLSD (viscous limited-slip differential), whereas the Lexus LS never did.
In terms of styling, the Q45 was a distinctive vehicle. Infiniti attempted to redefine the modern luxury sedan by offering a car with rather spartan amenities such as firm leather seats instead of cushy couch-like seats and no chrome or woodgrain interior trim. The Q45's grille also caused buyers to shy away because of its unusual appearance. A more conventional appearance (including a more conservative grille, woodgrain/chrome interior trim and cushy seats), more sedated performance figures, slower 17:1 steering (except on the Q45t, which retained the original 15.1:1 ratio), and a dynamically smooth suspension were all added in 1994 to make it a more status-quo luxury sedan. Thicker glass, keyless remote, auto-dim rearview mirror, dipping side view mirrors, an improved transmission heat exchanger and external ATF filter, new oval intake ports and revised disc injectors, lower ratio 1st and 2nd gears, fog lights, and metal backed camshaft timing chain guides were added in 1994.
The Q45 came in three variations: base, Q45t and Q45a. The Q45t and Q45a featured a rear stabilizer bar (with the a model being larger in diameter) and both models having a 1 mm smaller in diameter front sway bar, rear spoiler, BBS Kraftfahrzeugtechnik AG forged alloy wheels, 4-wheel steering and Q45a featured also active suspension. HICAS and the faster steering ratios was discontinued in the 1995 Q45t model and the Q45a model was not imported in 1996.