P0303 misfire code for 1997 Ford Wind Star with 3.8L engine

Question:

This 1997 Wind Star is having a misfire code after the engine is warmed up. When scanned there is no coolant sensor code except this misfiring code. The engine has a lot of mileage but when we checked the compression, readings are all above 140 psi. No engine coolant was found in the oil and I think the engine is fine. testing the vacuum confirms that the reading is well above normal.

Testing the injectors shows the same reading and when I checked the spark quality while idling, I have a steady blue strong spark. I am now inclined to suspect that we might have a computer problem. Do you agree?

ATS Advisor:

There are a few tests you can do on this code: 1.) try switching the plug wires and see if the misfire code will change to another cylinder. 2.) did you clean the mass sensor? usually this will not cause a misfire code. 3.) tried disconnecting the egr valve? if misfire stops, then egr system is faulty. 4.) if all of the above fails, remove the intake plenum at the intake manifold and most of the time, the seals and O rings for this plenum leaks causing a misfire code when hot.