vacuum advance/retard
 

how do you test the dual diaphragm vacuum distributor? i replaced all the questionable vacuum lines and any others i could easily get to anf no luck with the idle. so i tried disconnecting them one by one with the car idling to see what it would do and the only one that made a difference was the top line to the unit on the distributor. both did have a vacuum though, but when i disconnected the top line the idle dropped to 650. any ideas? if i need a new one, where could i get one and how much do they cost?