I had my spark plugs out recently because I was bored on my day off and figured I'd see how they were wearing after 40k miles of use. Plugs looked excellent but while they were out I figured I would peer down into the combustion chamber with a flashlight and see what I could see. I wasn't surprised to see carbon buildup on the tops of the pistons(what I could see through the plug hole at least.) I've got a little bit of a rough idle, it isn't erratic, rpm stay the same, but it's enough to be noticeable. My truck has become a hobby and I figured I'd like to take a crack at cleaning up some of the crud on the pistons. I don't usually buy cheap gas, 99% of the time I fill up at chevron, unless the fueler truck is there stirring up any junk in their reservoir, then I go a few more blocks to the next one. I'm not convinced on seafoam or any other cleaner that goes for $9-$15 a bottle. I've heard of people using water introduced into the intake manifold in small amounts while the engine is hot and at ~2500rpm. Supposedly this is an effective practice and perfectly safe if done right, but I'm understandably a little hesitant to put water in any amount into my combustion chamber. I've got a vacuum gauge rigged up in the cab of my truck, so I could probably just cruise down the freeway and use the vacuum hose to suck in some distilled water; most likely with something very constricting on the hose, like one of those needle fittings used to inflate basketballs. So what are your thoughts? Anybody done this themselves?