I'm not sure if this would relate to you at all, but I drive an accord. If the oil gets too low, vtec wont activate and it'll set a limiter at 4k..
So my guess is check oil level. if it's low, fill er up and see if that fixes it. if it's fine, check Vtec screen filter. Vtec solenoid is at the back of the head, passenger side, and looks like a grey cylinder object thingy.. There's 3 bolts holding that on, and there's a screen inside. clean that and reinstall. If that didnt fix it, check the bottom of the oil pan for any dents.
Beyond this I wouldnt have a clue.