Honestly, the best fuel system cleaner you can get is Lucas FSC. Lucas uses a base formula that mimics gasoline so it burns better and isn't bad for your car. It is made thicker so it coats everything with its detergents to clean it out. Never had any problems and nobody has come into our shop with problems from it either. I, personally, use Lucas every time I fill up but the recommended is every 2-3 fill ups. You should try Lucas Heavy Duty Oil Stabilizer as well. The added friction from an underperforming oil can lead to excess heat thereby increasing NOx. Next time you do an oil change, put about 3/4 of the bottle in it. As you lose oil or it gets low due to breakdown, add the rest of it.

Now about those plugs, as I have said before, platinum plugs burn the hottest and generate the most spark due to the low ignition point for the metal. The issue with platinum plugs (ANY plat plugs) is that the tips wear out much easier from being so readily sparked and will not burn off the gas as well as it should leading to excess carbon buildup. Go with iridium plugs OEM. That's what I have and I have practically zero carbon buildup (I check it every 3,000 miles at the oil change). Iridium is a stronger metal, less prone to wearing out than platinum. Yes it has a smaller spark potential but it also doesn't wear out as quickly as plats. You have a sustained spark for the majority of the plug. Platinum plugs also have a problem with the tip literally being blown off by the spark and that is never good. Platinum is not a very strong metal when used in plugs. Reason being, the metal is stretched thin to make the tip which weakens the metal and once it gets really worn, the tip blows off and can do massive damage to the engine i.e scratching the cylinder walls/piston heads, imprinting in the walls/heads, damage to the valves, etc. Besides the obvious damage your vehicle will now run terribly and if one is at that point the others are soon to follow.