new to mustangs,need tuning help

When it comes to late model EFI cars, modified engines generally need to be retuned by someone who understands the required changes. On the EEC-V cars (94-04), the spark timing is calculated by load. Load is calculated by Mass airflow, rpm, and cubic inches. Any changes to MAF or cubic inches requires a retune. On 05-up cars, forget it. Everything you do requires retuning. They are very sensitive.

Luckily, you've got a fox to work with, which is remarkably forgiving. Spark timing is an rpm-based calculation, so load doesn't affect it. Changing base timing settings changes all the spark tables globally. So adding 3 degrees base adds 3 degrees to every part of the timing maps, including the WOT total timing (which is 26 degrees total if your distributor is set to 10 degrees base).

Your main complaint right now is idle. The larger camshaft dilutes the intake charge due to the increased overlap. That means more idle airflow is required to compensate. What's happening to you is that the motor isn't idling fast enough, so the computer raises the idle (via the IAC) to compensate. But then it overspeeds, and the computer cuts the idle quickly, which drops it too low, so it raises it quickly... as you can see, idle hunting ensues.

The cure for that should be in reprogramming the idle airflow tables in the computer. But on Foxes, you can get away with increasing airflow thru the throttle body in other ways. You could open the throttle plate more, but that would put the TPS sensor higher in voltage, which screws you up. It needs to be between .9 and 1.0 volts at idle, regardless of where you set the throttle plate at idle. You could modify your TPS sensor to make it more adjustable, but that's a hack. You could drill a hole in the throttle plate instead, but that's trial and error and if you overshoot the hole size, you won't be able to get it to idle down.

Ford Racing used to make an IAC spacer that had a screw in the side of it, which leaked air from one side of the throttle plate to the other side of it, just like the IAC does, except you control this extra leak with the turn of a screw. That piece would be ideal for your situation, to fix the idle air problem. An induced vacuum leak might also work, but the leak would have to get it's air source from the air intake tube, otherwise the MAF meter won't be measuring it.