I just Seafoam'd my 08 Pathfinder today. The dealership told me I needed a $155 fuel injector cleaning, told them no, and bought a can of Seafoam ($10).
Pop open your hood, the power brake booster is located right in front of the driver dashboard, mounted on the firewall. The vacuum hose is the black tube coming out of the front of it. Pull it off and start up your engine. Let the vacuum hose suck out about half the can of Seafoam. Don't completely submerge the hose in the fluid, just let it gradually suck it out. Your engine may misfire a few times, which is normal. Turn the engine off and let it sit about 10 minutes. Then, take it on a drive - depending on how much carbon built up, there may be a lot of smoke coming out of your exhaust, or none at all. Then, fill up, and pour the last half the can into your gas tank.
My Pathfinder's idle is a lot smoother now. There used to be a noticeable vibration in the steering wheel when stopped at a light, but it's completely gone now.