I received some codes from my 1996 Seville/STS by holding the temp/ off button. Can someone Please help me to find out why I have a misfire/idle issue with the car? When Idling the car will chug slightly and sometimes when accelerating you can tell a piston is missing/not firing. The codes are as follows.


PC0300 - I think this is " Misfire Detected"
PC0603
PZ1558
PZ1971
PZ2471
IR1740
IR2255
IR2560

Does any of the does indicate a problem with a specific cylinder?

 

I replaced the spark plugs and it now doesn't chug as bad at Idle, which I don't understand. I really need help though? Does anyone know what I should check next? It only chugs when it is at about 750 to 900 RPM. Should it be Idling over 1000RPM? What type of issue only occurs when idling?