None of those things will cause white smoke, but spark plugs and wires are always a good investment, especially if they have a lot of miles on them. Some running problems can be solved by cleaning the mass air flow sensor and even the carbon from the throttle blade, but the symptoms will be considerably different than what you've described.
STP is a "viscosity index improver", meaning it makes the oil act like a higher viscosity oil. You can accomplish the same thing by switching to a higher viscosity oil at the next oil change. Oils today are really good and the additives do a much better job than they did 20 years ago, so there is little to be gained by using this type of chemical. If you DO use it, it's important to pour it in slowly while the engine is running and warmed up, otherwise it will form a big glob in the bottom of the oil pan and just sit there. STP will coat engine parts too so if any metal chips show up, they can get trapped in it instead of getting carried away to the filter. Those chips can be released later and potentially cause other problems.
Sunday, October 12th, 2014 AT 2:31 AM