Possible fueling issues?

phunk

Its most likely a tune issue... either tune or throttle bodies. Assuming you do have an intake manifold leak, while this would increase engine speed and lean out A/F a little at idle (o2 feedback should correct for this though, and show up as heavier o2 compensation that could be logged), I see no reason the engine speed should not be able to remain stable... for an intake leak is accomplishing the same thing as increasing throttle a tiny tiny bit. It shouldnt struggle to accommodate tiny intake leaks... Think of the PCV system, essentially an un-metered intake leak right there - sucking in that crankcase air.

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