If you feel that the price you were given to "tune up " you car is too much then by all means have at it and do it your self. I do auto and truck repair for a living and hear it a lot , wow it costs how much? shops factor in rent tools electric insurance what they pay the employees etc. it might be an easy job it might suck. do it and then tell us all how you made out. just remember the shop you went to is in business to make money. im quite sure if they did not need the money they'd be fishing instead. not to say there isn't crooks out there who will screw you but I like to think most are honest. its tough out there