That is interesting. Could be the 'cheap' egr valve was made with a weak spring.
I removed and cleaned mine months ago. It held vacuum and when I moved the diaphragm up it did affect the engine at that time. And there have been no codes. CEL does work.
I also plugged off the vacuum line to the egr and drove it a couple of weeks like that with no difference felt.
I tell ya, when it stumbles at low idle it feels as if it was loading up on fuel but since I cannot log it at those low speeds, I can't tell if it's a low idle or over rich condition. It never smells rich though.
Can this iac operate "out of range" so to speak?
I know the ecm signals movements of the iac.
This low idle and stumble is what made me start freshening up under the hood in the first place. It's why I turned up the idle speed screw, which cured the low idle stumble and die problem but caused the high idle on every startup.
So, I'm back to square one.