Additional Checks

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

If the loss of power is above 6000 RPM, check Rocker Arm Oil Control system for the correct operation. See DTC P1693: ROCKER ARM ACTUATOR SYSTEM STUCK OFF under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 1.8L VIBE article.
Check the Powertrain Control Module (PCM) grounds for proper locations and clean, tight connections.
Check the generator output voltage. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.