I have a 1986 2.5 w/ac and auto. My question is it seems like when the alternator is cycling to charge the the belt squeals. I think that is ccausing the erratic idle when sitting at stoplights also. I do not drive the car much at night but last ight I was out and with the headlights on it didn't seem like I could get the belt to stop squealing. When I turned the lights off everything was normal with no squealing. Could the alt. be bad? How hard are they to replce? It looks like a bear of a job.

Replace your alternator belt.

The belt is new. I put the good gates belt on a month ago. I adjustd the ension also.

If the belt is new, tensioned correctly, and no issues with it otherwise, then you need to check your alternator bracket and make sure it is not cracked or bent.

The Duke has the steel bracket that runs overhead. I have seen those crack before. It throws the pulley out of alignment.

You can even pull the belt and try some sandpaper on the pulley to see if that helps.

Oh... Turn the alt pulley by hand without the belt. Does it spin freely or does it bind up at all?

If it binds up for any reason with no belt on it, yes. Change the alt. If it spins freely, then it is most likely good, and an alignment issue is causing the squeal.