2004 Suzuki Vitara

is there a check engine light on?

no

ok, then you may just hav some basic things you need to do here, if you havent done plugs and wires, that would be a good start. also I would check fuel pressure just to rule out the fuel pump and filter and pressure regulator as being the culprit. are you experiencing any black smoke? also change your air filter if you havent already, touch bass with with me as to what you've done already