Could just be an exhaust leak, before your a.f.r. o2 sensor. Every time my 2 previous manifolds would crack, my numbers would jump all over the place. What kind/type of manifold do you have, have you ran across anything that would jolt the car fairly drastically? Where is your a.f.r. o2 sensor located? Chech your gaskets as well.
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You know, somebody actually complimented me on my driving today. They left a little note on the windshield, it said 'Parking Fine.'