rough idle..revs on own at stop light.. alternator??

[socalfocus]

hi .. i have a 2001 zetec zx3.. i just came back from the ford dealership and they could not find what was wrong with the car except for saying that for sure i would need a new alternator.just recently when i stop at a red light the car revs on its own.. it stays underneath the 1,300 rpm mark but it fluctuates up and down.. when it goes down the car shakes very very lightly but the baterry light comes on for a split second like the cars gonna shut off but then before it does it comes right back up..also when it does this the interior lights and headlights fade as it revs up and down..as it reaches the low point..i thought cleaning the baterry would fix it since it has some blue foam where the positive side of the baterry hook up is..but it still did it after..it drives fine when its on the road of couse..but at stops seems like a gotta rev it while im at the stop light to avoid it doing that and me scared of it just shutting off...ford said the baterry was fine tho.. i have a amp, subs and a kenwood touch screen tv.. the ford people said it prob messed up the stock alternator not having a capacitor as well..but he said the idling like that has nothing to do with the alternator and i would have to bring it back in to get a drivability diagnostic at 100 dollars in addition to the 50 i payed today only to be told i would need a alternator.. any different suggestions as to what the problem may be from anyone who has heard of this???

[Mustangman25]

All I can say is that I agree with what they said... dimming lights is most likely just a result of your alternator not being able to keep up with all your aftermarket equipment.
As for the revs, the rough idle sounds a lot like I experienced for a few months. I changed out the plugs and used low resistance wires and that helped, my next step is to take care of the PCV, but it's a real PITA to get on the Zetec, as it's under the exhaust manifold. Just a general tuneup may be worth it, to see if it helps at all, though it probably won't get rid of all of the roughness, just some of the major stuff. HTH

[nose-gobblin]

Make dure ur plug wires areent crap, then make sure your volatge regulartor isnt disconnected this can cause a wierd voltage flux