What kind of plugs and wires did you buy?  It is recommended that you stick
with original Motorcraft parts and not aftermarket, such as Bosch.  Why did
you change the original parts, was the car acting up beforehand?  Any of the
original plugs not burning correctly?

The first thing I would do is take one of the old spark plug wires and pull
the new ones, one by one and temporarily replace the new part with the
original.  Start the vehicle each time you switch the plug wire.  Unless all
4 of the new wires are bad, this should isolate the problem if it happens to
be a bad plug wire.  You know you've found the right wire if the car starts
running smoothly again.  Make sure you change out the coil wire as well.

If nothing happens with the new spark plugs installed, switch them with the
old spark plugs and retry.  If after you change the new plugs back to the
old, the car starts running fine again, one of the new plugs are bad.

This may take some time, but you said the car only started acting up after
the spark plug and wire change.  Thus, that pretty much tells me one or all
of the plugs or plug wires are bad.

Good luck.
Sharky

In your case that's probably correct.  Not always, though.

http://www.autotap.com/articles/OBdII_and_emissions_testing.html

It still couldnt hurt to try to read them out.  Might be a hint, there.