Welcome to the club Jason, I'm afraid there are no easy ways to improve the is200's power. Only way to get worthwhile power increases involve turbo/supercharging or engine swaps.
Only thing easily done is usual exhaust. air filter change, but gains if any are negligible.
Camshaft bank 2 sensor is pretty easy to change and is on the front cylinder head on the right hand side as you look under the bonnet and is fixed in by a 10mm bolt and a multiplug. These are quite common faults.