The head gaskets - the head gaskets and everything else under the sun!
I bought my used '95 Ford Windstar only 2 months ago and it has been in the shop for one of those!
I had it exactly 3 weeks to the day I bought it when the head gaskets blew. It broke down on the Cajon pass (a big mountain pass in California). The pass is so dangerous that CHP pays tow trucks to haul broken down cars off of the pass for free!) with me and my two small children in it.
I got it back and drove it for 4 days when the engine light came on. Now the dealer has had it every since. They have no idea why the engine light keeps coming on. At first they told me that the fan shut off causing the engine to blow one of the gaskets. Now they can't figure out what the REAL problem is. They can't fix the thing. It keeps ripping up the gaskets though! DO NOT BUY ONE! PLEASE HELP if you know why the engine light does that!
It's your air flow meter.
Same thing happen to my 1995 Ford Windstar Van.
Good Luck.