So I just bought the 4th V8 Stang I have ever owned, 3rd 5.0. It has 49k miles. Immediately I put new plugs, wires, cap, rotor, air filter, fuel filter, oil and filter, and brand new IAC from Ford. She is 100% stock underhood, o/r x-pipe, flowmaster catback, and 4.10 gears (assume). Problem is...