I like to use seafoam, but what i do is find a vaccume hose and use it to suck up the seafoam and make the car stall. then i let it sit for about 10 min then start it back up,, the car will smoke out all your neighbors when you first start it but it works for me, then i add it to the gas tank..

i do this once a year or when i first buy a used car. works great for me,

ive used seafoam and didnt really notice a difference but maybe others have.