I've noticed that I have a slightly rough idle when the air pump is on. I can hear the air pump pretty good when it's on (EDIT added detail: if I'm near the engine with the hood open). I can feel a decent shake which almost feels like a slight mis-fire while it's running then the engine is as smooth as a top once the air pump clutch disengages.

Any ideas?

fwiw... I'm getting a pretty good rotten egg smell when I floor it. I can smell it in the car even with the winders closed.

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