Mine also does this after it's warmed up. It won't catch itself coming down to idle speed very well unless the AC is on, which bumps up the idle speed by about 50 rpm and it really seems to help. It feels like a vacuum leak issue to me, but i'm in the same boat where I'm not throwing any air/fuel codes, or any codes for that matter. I too will eventually test the fuel pressure.

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Black Sapphire Metallic 2002 4.6is