2000 Mystique alternator?

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Hi Folks. 2.0L 4-banger/Automatic/AC. I'm trying to help my daughter get her car running right. She was told there were codes for plugs/plug wires and one for alternator. She replaced the plugs&wires, but nothing changed. I idles vert badly. Once it gets up in RPM, it's fine. The Battery light is not on, but the bulb is ok. She said all this started after the car went through a big puddle, but that was months ago. My question is about what Alternator the thing needs. Ford manual (Haynes) claims the Mystique has a 130A output alternator. When I used parts search engines, I see 105A/110A/120A/130A alternators for that year Mystique. Huge price difference in the 110A to the 130A unit. She bought a junkyard Alt some years ago to replace the OE unit, so whether or not the junkyard unit is right or not, I can't say since the OE unit is gone. I can see a 130A Alt in a 6-cyl, but in a 4-cyl?? Removing the alt isn't a piece of cake. I haven't checked the car out since it's a 100 mi drive, so I'm going on what she's told me. Why would an Alt code cause the engine to idle badly and what would have gotten wet months ago to cause the problems in the first place? Certainly it would have dried out by now! Long-distance diagnostics is difficult. Any help/info/advice would the greatly appreciated. thanks from Texas