The Toyota 2.4L isn't commonly tuned. That engine is in hundreds of thousands of really boring cars, and a few fun ones including the Scion TC.
Unichip makes a chip for the Scion TC, it might or
might not work in your car. According to Unichip it "Adds up to 14hp &12ft-lb" which is a calculated number, your mileage will very.
http://www.unichip.us/vehicle/vehicles/ ... ion-tC-24L" onclick="window.open(this.href);return false;
The tune on the chip requires an intake and cat back exhaust. If you have a different setup you'll need to ask Unichip or Unichip tuner to change the programming.
It's up to you to figure out what your goals and budget are.
Is spending $X for Y HP worth it?