surging below 3000 rpms
 

i have a ka24e motor, its mainly stock, all i have is a cone filter.
at low rpms it surges really bad, and as soon as i hit 3000 rpms it starts running normal. its like hitting vtec or something hha
i have no idea what it can be.
i have got a new air filter, fuel filter, cleaned intake manifold, new spark plugs, replaced o2 sensor, and i don't know what else to do.
anyone know what might be wrong?

thanks