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Old 10-15-2004, 02:25 PM   #2
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Matt -

The combination of the hissing sound, the fact that it only occurs after warmup, the rough idle - yes, it ceratinly sounds like it could be an air leak, and the manifold is one of a few likely candidates.

One thing bugs me, however. For a fairly large air leak (large, totally subjective term, but I mean it's large enough to HEAR above the engine noise!) I would expect a Check Engine light with a code P0171 (system too lean bank 1)
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