Originally Posted by ctechbob
I think he's referring to the EGR Valve.
https://www.samarins.com/glossary/egr.html
Usually looks like that in Honda's. MOST of the time it is fairly easy to get to and remove.
Sorry for that, I did mean valve. There are several videos on where they are and how to remove, clean, and replace them on Youtube. On a Honda 2.4 it is up front on top to your right as you are standing in front of the car (vehicles left) and very easy to do. If you reuse the old gasket you probably should use a very thin coat of red RTV sealant on both sides of the gasket, but with 100K miles you probably should get a new gasket.
You probably should start with the EGR valve. If it is not operating properly due to carbon buildup a good cleaning could be all that is needed.
I am not a ASE certified mechanic, but from what I have read:
1) Problems at low rpms (not much throttle) are more likely to be the EGR valve than the passageways, though it could still be the passageways.
2) Problems at cruising speeds (higher throttle) are more likely to be the passageways, though it could still be the EGR valve.
And of course since the EGR valve is super simple to do on that engine you probably should do that first before thinking about doing the passageways that are a harder job.