2004 Honda civic ex check engine light?

I'm having a code that reads p0 2646 the problems that the car has is when you get to 5000 rpms the vtech doesn't seem to kick in the car kinda shakes so I just et my foot off the gas and slowly get to speed. So just want to know what part or parts to check and possibly what part I need to change. But note that this problem wasn't happening before a head gasket change?

http://engine-codes.com/p2646_honda.html

Hi it is not the head gasket if only it was. This is wear in the engine. Hardly so surprising given the mileage it has done which you fail to mention. My guess would be you know that is why it has now come to this point in time it needs a new or re-conditioned engine.

This is what happens when you don't do oil and filter changes every 3,000 miles if using conventional oil in your motor or use Mobil 1. When oil isn't changed soon enough it forms a tarnish that clings to the oil passages, cam actuator for advancing the cam timing and the solenoid that controls when the oil passage opens to make the VTEC work. To fix this the actuator and solenoid needs to be replaced. If the mess is bad enough the cylinder head will need to be removed, disassembled, and put in a hot tank.