try a map first.Do a compression test to see if you have a valve bent or sticking.

You can also see what cylinder is missing by removing one plug wire at a time.
If you get to one and rpm will not drop or the engine will not die that would be the problem cylinder.

You might also have a vac leak spray brake clean or carb cleaner around the intake and all vac hoses if engine rpm increases where ever you spray that would be where the leak is.A vac leak confuses the map.