DAMMIT RAY ! (old indian saying)

Higher idle does sound like it’s a bit leaner.

But. On our E body, it started to do that. I went through same things.

Then I figured it out - the throttle linkage was ever so slightly binding in the casing. Just a very small difference in a small bend in the routing because of the intake differentiation. I put a heavier spring on it and solved the issue. Just an idea.