I don't use any cleaners or fuel additives in my cars anymore, including Seafoam!
My secret...? Shell gasoline V-power 93 in my SL and The Mark, and regular unleaded in Wendy's mini van, and her son's v6 Mustang.
I kid you not. The stuff really works. I had a lazy o2 sensor in both the SL, and the Mustang that would set off the check engine light and throw a code in both cars. One would think that I should change the o2's and be on my way... But no... Run two tanks of Shell gas in each car, and no more cel's or codes. The cars both run better, and smoother too.
I was a firm believer in BP fuel for years, and would drive out of my way to get it. Not any more. I drive out of my way for Shell fuel now.