I don't think fuel pump or accumulator would cause your problem. The OVP could be the problem, but age of the car, hesitation off-idle AND erratic idle sounds to me like the airflow meter potentiometer. Check plugs too to see if improper mixture could be the issue.
Steve
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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7
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