Check Engine light is on. I'm troubleshooting.

While trying to find any vacuum leaks with a spray can of quick-dry plastic-safe cleaner for electronic contacts I decided to do a little cleaning around the sparkplugs.

When I aimed the red plastic spray tube down into the recess for the #3 plug the idle smoothed-out.

I pulled the plug and found that the top connector was bent. Aha! I replaced the plugs. The plugs were tough to remove. New plugs, tough to install.

Okay: with new plugs, I got the same effect when I sprayed around the #3: Smoothed idle.

I took the plug out. Cleaned around the hole. Put the plug back in. Same thing when I sprayed.
Took it out again. Looked for clues. Cleaned the Bougicord F. Carefully applied some dielectric grease. Snugged the plug back in. Tried spraying again --- same thing, idle smooths out but less... Took the boot off. Cleaned it again. More dielectric grease. Tightened the plug (more than I liked...) sprayed again... got a briefer smoother idle but still noticeable.

I thought "is the cleaner getting into the EGR tube below?" Sprayed the tube directly: nothing.

What is it? What am I missing?