+1 the risk of a "check Engine soon" light and needing to replace O2 sensors has me avoiding Seafoam. Immediately prior to an oil change, consider using a engine cleaner (usually has Kerosene in it). This does a good job of dissolving bits in sludge and varnish in the engine. The label should instruct "pour in engine and run several minute before draining oil". I used some yesterday as part of my oil change and found the engine runs like new.
Techron will do the same cleaning and good carbon cleaning, but you need to use it over a longer period of time.