I really am opposed to seafoam or similar products. Unless you use them every few thousand miles, all your doing is knocking buildup from where its safe and not in the way to somewhere it can seriously harm an.engine. I've seen several cars get junk trapped under the valve and cause serious damage to the valve, head, and piston. I also wouldn't want that crap in the cylinder either.
OP- sounds to me like plugs / coils oor possibly an intake manifold leak. Tune up time.
2003 Mach 1