code(P0301)#1plug miss fire,still miss fire's after tuneup.

What i do to check a misfire, is I ->#1check compression in that cylinder then #2 verify that the wires and plugs are good and not defective. Did the van run fine before you did the tune-up? Because if it did, you may have a defective part, or something came loose. Were the wires replaced as well, because that is important?