This has been posted numerous times, and after watching the episode and knowing it was th eend of the season, I'm gonna go with that there is no new ep coming in four weeks, that basically Trey and Matt are poking fun at Series that do Cliffhanger episodes where you have to wait and see...
Plus do we really want to know who cartman's dad is? It would screw up the chemistry we have right now with the characters. the humor wouldn't be the same if say , Chef was Cartman's dad...
just my $.02
According to the Comedy Central web site, on 3/25 they are going to play episode #113, which we already saw, all over again. They will re-play that a total of four times, (with the "four weeks" part at the end suitably altered, I'll bet) and then the following Wednesday will be April 1st.
With the obsession that Matt and Trey have for holidays, the fact that the episode is going to fall on April Fools Day will not have escaped their attention.
Things are becoming clear now.
http://www.comcentral.com/ - click on "TV SCHEDULE" and select South Park.