2003 Honda Element code P2646

Help anyone. I have a 2003 Honda Element with the P2646 code. Im using Autozone for my diagnostics. The first suggestion was to replace the knock sensor. Completed. Code still there. Next suggestion was to replace the Variable Valve Timing Pressure Switch. Completed last night. Check engine light came switched off after several minutes and returned several minutes later. All along this condition has been accompanied with very intermittent loss of power or slight bucking during acceleration. Anybody have any ideas?