Sounds like a misfire or an air leak.
First thing to do is search for an air leak in the vacuum hoses and intake system after the MAF. The brake booster hose has been giving a few people problems lately, so be sure to check that one too.
Next try new Motorcraft replacement plugs & wires if you haven't done that lately. These cars seem to prefer Ford Motorcraft ignition parts, nothing else will do as well.