Hi guys, I have a 99 mustang V6 that has always had a problem with missing at speeds of 40 to 60 mph, which shows up especially on hills. It has new plugs, plug wires, air and fuel filters. It idles perfect. Someone told me to clean the idle bypass valve which could cause this problem and check it for operation which I did. It cycled fine. Any other things to check?

 

coil pack if not fixed then new fuel injectors, and still not it do a compression check