Alternator or something else electrical?

elkulioso

So I just bought a 2006 Town Car. Elderly driven, only 90,000 km (Canada) when I bought it. It had sat for a year and a half before I bought it. Got it saftied and all and then the next day the battery lets go on me. Runs like a charm now except for this little problem I'm having with the RPM's. All of a sudden when I'm sitting at a stop light the RPM's will dip down from 500 RPM to about 350 an come back up. It doesn't really feel like the car is going to die but one time I did notice the lights dimmed a little bit. (This was all after getting the battery replaced). Now, it hasn't been doing it a lot lately but I do still see it happening every once and a while. I went and had the alternator tested and the garage said it was charging at 15.5v which is kind of high, but he wasn;t sure if it was specifically alternator related. Just don't want to leave it too long and burn my system out. Any help is appreciated. Thanks!!!

Mr_Shiftright

Could be the alternator. It has a voltage regulator build into the back of it, and 15.5V is too high, so something is up. Very often, cheap aftermarket alternators, if installed by the previous owner, don't work right on cars like this.

elkulioso

Can I replace just the voltage regulator or do I have to replace the whole alternator? It is the original Motorcraft alternator on there. @Mr_Shiftright