Cadillac Repair: 1990 Cadillac Sedan Deville, 4.5 8cyl, vacuum hoses, spark plug wire

Question
QUESTION: I just bought this vehicle and it seems to idle rough and will die at lights or when I slow down.  When it does run it runs well.

ANSWER: Remove the air cleaner assembly so you can see down the throttle bore where the air goes into the engine. If it covered with a blackish residue, Use an aerosol cleaning agent to clean BOTH side of the throttle plate and the throttle bore area and see if this resolves your problem

usually the residue builds up and will not let the throttle plate close tightly within the throttle bore thus causing the engine to stall.

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

QUESTION: Thank you very much.  Took the car for a 7 mile ride afterwards and it did not die once.  Hope that tomorrow when we need to go further it continues on this path.  This car continues to idle very rough.  We were told by someone else today that the map sensor was our problem and we spent $50. to replace it with absolutely no change in the car, it was only after your reply that it did stop stalling out everytime we slowed.  Any ideas on the rough idle.  Thanks again so very much.   Earl

Answer
Could be a faulty spark plug or spark plug wire or a cracked/broken vacuum line. Spray all around the intake manifold and on the vacuum hoses with an aerosol can of CARBURATOR CLEANER being very careful to stay away from electrical circuits and when the fluid hits a vacuum leak the idle will change.