your 2003 should have the same setup as my '02 2.0 4wd 5door which acts as a company demonstrator - Im a wheel importer/distributor, and needed the cabin room inside, and loved the look so.....
To start with, loose the factory airbox on top of the motor.
get a cold air feed pipe made up from alloy tube, or 3in exhaust tube and run a k&n, Simota or similar pod type filter low down in front of the gearbox.
you need to put some sheilding between the pod, and the exhaust to block heat, and create some form of ducting to catch cold air from in front of the radiator, or from under your front bar.
whatever you make up, ensure that the risk of it scooping up water or snow and flooding your pod filter is minimised.
Im currently making one up where the pod is straight over the top of the gearbox, with seperate ducting right up to it from underneath the front.
second mod would be to free up the exhaust. on a late model rav, the entire system from the bottom of the Cat Converter is shocking.
get a mandrel bent 2.5" pipe made up with a decent free flow muffler in the middle, and a straight through performance style can muffler at the rear. i dont recommend going over 2.5in for a 2.0l motor unless you've discovered a bolt on turbo kit.- and yes these are very rare indeed - ive looked.
These 2 options should see a very noticable leap in performance.
a popular mod is to get a set of HKS earth straps for the motor, these are supposed to improve the electrical spark to the plugs, and again should increase responsiveness and low end power.
from there, synthetic oil, with a top grade filter will also help.
From there, the easiest way to maximise your performance is ironically on the outside. get a quality set of FORGED alloy wheels - mostly seen on import racers. the lightweight of these rims, with a set of suitably rated tyres ( not Z rated unless you drive at 100mph everywhere) will release the existing power better. with better acceleration, mileage and less jarring over road bumps.
Racers use a lightweight flywheel to lower the centrifugal drag on the motor to go faster, the weight of a wheel is heavier, and further out, and theres 4 of them. it will be like driving a 3.0 instead of a 2.
the only downside is Forged wheels dont like hitting things like rocks....
if you want more Rav info have a look at
www.rav4world.com its an internet group that do nothing that play with Rav4's.... happy hunting