Changed alternator and now...
 

Juan (username) changed his alternator the other day. he just calld me telling me that ever since he changed it the car diesels out a lot and it idled a lot higher than it used to. ive never heard of an alternator doing anything like that before. what could it be?

their is so much info about type of car year ect ect thats missing to give any sort of help - jz

crap that's right. 85 trans am. 305 h.o 5 speed. bone stock. bout 80,000 original miles

I'm thinking he's got a major vacuum leak somewhere. Did he forget to reconnect one of the vacuum lines he pulled off to change the alt? Or maybe he knocked one loose?

look for a cracked vacume line

yeah id check for vac leaks as well...easy to do
grab a propane torch, turn on the gas but dont light it.
start the car and run the torch with the gas valve open around
the vacuum lines, once the idle smooths out youve found your
leak.

also check the size of the alt pulley compared to the old one,
sometimes aftermarket alt pulleys are huge and causes some probs,
but this sounds like a vac leak cause of the dieseling

wouldn't it be safer to use like carb cleaner? propane sounds haggard

carb cleaner will stall the engine out...and make old plastics even more brittle
propane just smooths out the idle wherever the vac leak it...it gets sucked in
and eventually combusts. gs