I've been hearing and reading about how seafoam was used and improved engine performance. They say to pour 1/3 into brake booster line, 1/3 into the crankcase and last 1/3 into the fuel tank. Any of ya'll tried this on your 4.6 or 5.4? My '03 5.4 has 95000 miles. I've been pouring in injector cleaner in my tank every 3000 miles since I've owned it since new and wonder if I need to do this since my engine starts easy and runs smooth. I'm getting about between 16 and 18 on the highway at 65 mph and my truck is 4wd w/ the FX4.
Take the intake ducting off and look down the throttle body with a flashlight, if it's black then the first thing you should do is spray it out with some Berryman's B12 chemtool. Spray just enough to wash the carbon away. Run the engine for a bit, and don't be surprised if it takes 3 or so tries to get it to crank up. After that I'd run a little seafoam through the brake booster just to catch the carbon that settled in the lower intake manifold.
If the throttle body is dirty that's a whole different thing. Take the whole throttle body of and clean it with a throttle body and intake cleaner. Spraying anything into the intake directly is a good way to hydro lock a motor. Here's a little info on additives: http://www.f150forum.com/f7/411-additives-63987/