In my experience, there is only one product that really works: Techron. You will need to go through at least one tankful of gas. If you are going to go on a long drive, that's the best time to use it. You don't really want to add it and just let your car sit, or you may have to go through a second application (once the first tankful is consumed).
Just keep in mind that Techron does a great job in cleaning the system, but it isn't going to make any Spider faster than when it was new, and these cars are not fast off the line. Once they get going, they are great...
Best regards,