Cadillac Repair: 1990 Cadillac Sedan Deville missing / sputtering, spark plug wires, intake manifold gasket

Question
My 90' Sedan Deville will sputter and hesitate when I slowly accelerate from 40-45mph if it is under load.  If I push harder on the accelerator and it shifts down, the hesitation/sputter will go away.  The sputter will return if I slightly accelerate if it is under load. Also at idle, in gear, it also "misses".  Upon quick acceleration, it doesn't hesitate/sputter at all.  It does have new plug wires, plugs and fuel filter.

Answer
Spray the intake manifold gasket and vacuum lines for any signs of leaks using carb cleaner. When you hit a leak the engine will increase in speed and will smooth out the idle.

CAUTION: Carb cleaner is explosive is saturated on an electrical component or spark plug wires.

With the engine running unplug, one at a time a single spark plug wire and see if the engine speed drops like it should. If you unplug one wire that does not change the engine speed or make the engine run rougher, suspect a bad spark plug, fuel injector or possible cylinder.