20,000 miles would not be enough for you to go back in there, but take the hose off and take a look. If it’s gunky on from the outside, the gunk will be much worse inside the butterfly.
I had a slight drop in RPMs every 32 seconds with a hot engine at a stop light. With the AC, headlights, and other accessories on, that slight dip was amplified to something enough to stall the engine out. That came from a failing intake manifold gasket.
There’s a difference between the CPS and the CKPS. I’m sure you got the right one, the hidden one, but if you’re talking about the one looking at you when the hood is up from the passengers side, you don’t.
Clean the EGR again to see if it helps. I replace the darn thing. Was it giving you a problem, or were you just being proactive?
If the coils are originals, then that could easily be the culprit. Although it’s not all inclusive, check for cracks, or any damage to the rubber boot. While there, check for oil in the plug wells. If there’s oil there, your seals have perished. Lastly, replace the plugs while you’re looking around. If you can’t remember, then it’s time. At $3/ea and ten minutes of your time, it’ll be time well spent.