Well, I took my car to a dealer to have the codes read. They told me a Misfire code was what had triggered the Check Engine light. They could not replicate my problem, but told me that the third cylinder's spark plug wire looked damaged. They suggested that I replace the spark plug wires and spark plugs. This got rid of the problem. My only question now is: why was the car usable under 4000 rpm, if the problem was in the spark plug wires? This confuses me. Thanks again to those who responded, and to anybody who responds to this message!

Had the same problem on my old Ford Mondeo 2.0i (1996)

When going past about 4000rpm the car lost power and even started to vibrate.

Changed the spark plugs and spark wires , problem gone! It seems that the problem only shows when engine has to work harder , like over 4000rpm or driving uphill ...

This was a common issue with cars that commutes to and from work everyday my mech told me...Dunno if true for all cars but it sure was for the Ford.

// ermik - 1998 S70 2,5 SE 90K <> 1992 850 GLT 130K ** Both Auto Tranny - All equip !