A Dealership explained to me that a tune-up only consists of the plugs and plug wires(if they need to be replaced). What actually really kills you is the labor to do these things. I'm doing a tune-up on my zetec in a week and its costing me $40 less than what Ford would do it for. Zetecs are easy and will take like 20 mins. at the most.
For the carbon build up, louisw is right. Do it yourself, that way its done the way you want it and its much cheaper.
