Lack Of Power

Check fuel pressure. See BASIC TESTING - GS-R article.
Check throttle cable and then throttle body for sticking and binding.
Check Throttle Position (TP) sensor. See DTC P0122 in the TESTS W/CODES - GS-R article.
Check Intake Air By-pass (IAB) control system. See SYSTEM/COMPONENT TESTS - GS-R article.
Check air cleaner.
Check 3-way catalytic converter for restriction.
Check Manifold Absolute Pressure (MAP) sensor (if equipped). See DTC P0106, P0107 or P0108 in the TESTS W/CODES - GS-R article.
Check for contaminated fuel.