Ford Repair: Check Engine Light - Engine Vibration, engine vibration, sparkplug wires

Question
I have a 1999 Ford Explorer XLT 5.0L AWD.  When I get to about 40mph, the vehicle, coming from the engine area, vibrates rough until I get up above 45 mph.  Then, the check engine light came on.  I have never had this problem before, and I just came back from a trip where the vehicle sat for a week.  Any ideas?

Answer
Since the CEL came on, you need to find out what codes are stored. Until those codes are known, diagnosis is a shot in the dark. This engine had problems with sparkplug wires which may cause symptoms similar to yours, but without codes I will not recommend anything. The speed sensitive nature of the problem could indicate many things, including transmission.

Get your codes and we'll see what we can do.