Engine / fuel treatment and cleaners
My boss at work used to design bearings and stuff for automatic transmissions and knows everything there is to know about trannys and pretty much vehicles and engines. Today I asked him about engine / fuel treatments and cleaners to see if they actually work. He said that the cheap ones do nothing, but one that does work is the Techron one, it's around 10$ a bottle. He said anything with kerosene in it is pretty good. A crazy thing he said it that you can actually use ATF right in your gas tank and it will clean some stuff up and not hurt it.
I also mentioned SeaFoam and putting it in the vacuum line. He said he wasn't familiar with the stuff but said you could put injector cleaner in there too.