ok well my truck does have a slight rough idle.......... is it possible to be throwing codes without an SES light showing up......... should the SES light turn on with all the other lights when im first strarting up my truck......... oh and on the seafoam treatment how long should i wait to change my oil after pouring it into the crankcase.......... thanks again Hanr3

 

It is possible for the Electronics not to throw a code and your engine to run rough. I own a 1999 Pontiac Gran Am and it has a slight misfire which i pulled out with a scan tool but the SES light was still off. Some times it takes a while of driving with the condition to get the SES light to go off. The computer is programed not to go off every time there is a minor problem. It would not make for good customer relations, kinda like a hypchondriac going to the doctor for everyday aches and pains of growing old eg; skinned knee, small nick with a sharp kitchen knife. You can see how if the computer went off every time there was a misfire, take it to mechanic you start looking like a paranoid car owner.....but when the light does go off you should have it checked then....