At 1200-1300rpm @30-35mph the car surges or jerks.

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Runs well great power etc. At very slow speed in Drive rpm fluctuates up and down approx 150rpm 6-750 rpm. Check engine light comes on when slow running. Poor fuel economy. At 1200-1300@30-35 mph the cqar surges and jerks. Codes 42 - HO2S sensor voltage high/system rich. O2 sensor changed. rebuilt engine approx 20,000 miles