Pope Francis is not preaching a Marxist ideology because he believes that the wealthy have too much of the world's resources. Marxism is a very specific ideology, and it involves one or two more revolutions than the Pope probably is interested in. Pope Francis should, however, try to further educate himself on the economics of capitalism, as his blanket condemnations are both incorrect and misleading.
If I remember correctly Karl Marx was anti-religion and I really don't think the pope is anti-religion. I'm not familiar with the context of Limbaugh's statement or what particular remarks by the pope he's talking about, but even if the pope is preaching ideas that are similar to Marxism, it's certainly not pure Marxism.