In addition to the above items relating to a 94 model, you may want to check the cam postition sensor on this 96 engine; they frequently break internally and can give you funny intermittent driveability symptoms such as this without failing long enough to set a code.   The cam sensor is the little shaft driven component that mounts in the area where a distributor used to go.   Remove the cover and check for powdery rust inside, or metal flakes, or cracks in internal parts.   Note: if you remove it without marking it first, you will need an indexing tool to reinstall it.

   Check for any kind of small vacuum leak; smoke testing works very wekk.

   I am not sure if it is applicable to the 96 model engine, but in prior years the 4.6 engine had issues with oil pressure loss to the hydraulic timing chain tensioner which would allow the chain to slacken and throw cam timing off intermittently, especially at idle.   I think there is a Ford TSB on this, but I cant seem to locate it in my database.    If this is happening, it will set no service codes, but you may be able to catch engine vacuum becoming slightly lower or erratic due to the cam timing change when the problem occurrs if you drive it around with a vacuum gauge connected.