Iíve been using Berryman Chemtool B-12 for upteen years in all my vehicles. Itís the best fuel additive/cleaner Iíve tried.
I usually dump a can in a full tank of gas about every 6 months. You want to run that tank down, then immediately change oil and filter, because as it cleans, it deposits everything in your crankcase oil. So I always put in a can in the tank of fuel right before my oil & filter change is due.
Stale or bad gas can cause all kinds of issues. If the vehicle is not going to be driven much, you might consider putting in some Sta-Bil Storage fuel stabilizer.