About 3 monthes ago i installed a full exhaust system into my cobalt ss/sc and since then my gas mileage had suffered. I was told from alot of users here that i need a tune-up...i talked to the mechanic that installed erything for me n he said that it wasnt necessary n that my car's computer will adjust to the changes n if not i would have a check engine light...i havent had a check engine light yet (knock on wood) luckily...so should i really get that tune-up? n is it that necessary?

 

lol refer back to u other thread