Thanks for the input LarryBible.
I use the Bosch copper plugs recommended for the car, they come already gapped.
I cleaned the sparkplugs and the car feels like it gained an extra 25 HP, and idles much better. Still my concern is the plug at #5, it had plenty of caked-black deposit on it. The others were "clean" compared to that one.
I am starting to think that injector is "dripping" rather than "spraying".
I will be driving to NYC next weekend, and will try the "2 bottles of injector cleaner on one full tank - drive at 85 MPH for 7 hours treatment". Followed by an oil change.
