Cadillac Repair: 1991 Cadillac Eldorado, cadillac eldorado, heater core

Question
QUESTION: I have a stuttering problem with my 1991 Cadillac Eldorado. All the plugs, wires, cap, the coil pack are all brand new. I tried everything that i could think of and cant find the problem. What you think about it?

ANSWER: IS or HAS the CHECK ENGINE LIGHT on the dash ever illuminated ?.

---------- FOLLOW-UP ----------

QUESTION: no my check engine light does not come on. i know the heater core is plugged up and i am about to change it. maybe thats got something to do with the vacume or something with the motor.

Answer
This is a possibility. I would suggest either replacing the heater core and or remove the heater core hoses from the heater core fittings and put the hoses together to allow coolant flow to pass thru the engine without being obstructed by the plugged heater core.