hey guys i got a very bad idle problem when im sitting at stop light my car idles very bad and also very shaky?but in normal driving condition is fine its only when i come to a stop and starts to idle very bad i can see my idle rpm going up&down...i had my friend from work put it on the scope and turns out to be clylinder 5 that is missfiring so he told me to put a new spark plug so i did it when away for like 10mins then came back??......any ideas what it might be??. guys please help!!!!!!.....thanks