Four engine spec changes occurred on the 2003 Corolla, per Car & Driver, larger throttle-body, new intake manifold, new design catalyst, and lower final drive ratio.
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The 2003 Corolla still uses the 1ZZ-FE 1.8-liter engine found in earlier models,
but a larger-diameter throttle body has bumped peak horsepower up 5 hp to 130 at 6000 rpm, and the torque band has been broadened, says Toyota, by the use of a new fiber-reinforced intake manifold, which now includes a plenum.
Corollas use a
new-design catalyst with an ultra-thin-wall, high-density substrate to hasten light-off and improve performance. Also fitted is a new-generation starter with square-section wire windings and iridium-tipped long-life spark plugs.
Although the transmissions are carried over from '02 Corollas,
the final-drive ratio is lower—3.94 versus 3.72 on manuals, 2.96 versus 2.66 on autos—promising equal acceleration despite a weight increase of about 200 pounds. As is the usual trend with these things, the 2003 Corolla is longer, taller, and wider, with more head and hip room, a 102.4-inch wheelbase, and higher seats for easier access.