Golf III

Hello, I would like to know if someone can help me. I have a Mexican golf mod 97 and the problem I have is that to gasoline once it takes temperature, it begins to vary the engine revolutions, for example it is regulating 9000 rpm and suddenly starts to lower and go up the rpm alone ... if someone can give me a hand that has happened to you this or conosca of the theme to see that it can become ... thank you very much

Three things I think they can be dirty or with water, covered filters or rotation regulator or idle pump or worn