Ford Repair: Miss firing, 1997 ford aerostar, spark plug wires

Question
My 1997 Ford Aerostar 4.0 engine with A/C front and back.This engine misses firing most of the time. When at idle it is very noticable. With out of gear speed the engine and It appears to go away. Howaver, I believe that it still misses, can't tell verywell because of the noise. AT around 70 to 75MPH you can tell that it miss fires because it gerks. I have tested the plug wires and have replaced the plugs, has not helped.  

Answer
Mr. Lindsay,

If your engine is misfiring, it could be several things: 1) your spark plugs could be worn, fouled or not gapped properly, 2) a fault in the fuel or electrical systems, 3) faulty spark plug wires, 4) vacuum leaks at intake or hose connections or 5) uneven or low cylinder compression.

You said that you checked your plug wires and that you changed the plugs, did you make sure that they were gapped properly? Recheck to make sure that your new plugs have not fouled. To test your fuel and electrical systems, you will need to take your vehicle to a reputable dealer and have them place your engine on a scan tool. I would strongly recommend that you have your vehicle placed on the scan tool to exactly pin point the problem. Hope that this helps and good luck.

Ken