Hi. I have seen this once before on an Amanti. It was fairly difficult to figure out. The vehicle had erratic tachometer. What I found was a sensor called the Ignition Failure Sensor controls the tachometer. So I replaced that and the problem was solved. I wouldn't be surprised if this is your problem.
I will include a diagram to help show you its location. CLICK HERE for diagram. This should put you on the right track. Let me know how it works out. Thanks, Eric
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